Showing 1–50 of 58 results for author: Oblak, D

Memory-assisted multimode microwave-to-optical transduction

Authors: Ujjwal Gautam, Nasser Gohari Kamel, Sourabh Kumar, Daniel Oblak

Abstract: Microwave-to-optical quantum transducers will enable coherent interconnection between distant superconducting quantum devices. Ongoing explorations with several platforms have shown promising results at single-photon levels. However, in all these demonstrations, elimination of noise due to the concurrence of the weak transduced signal with intense pump pulses remains a challenge, requiring high su… ▽ More Microwave-to-optical quantum transducers will enable coherent interconnection between distant superconducting quantum devices. Ongoing explorations with several platforms have shown promising results at single-photon levels. However, in all these demonstrations, elimination of noise due to the concurrence of the weak transduced signal with intense pump pulses remains a challenge, requiring high suppression filtering setups. A memory-assisted transducer, on the other hand, offers a versatile approach that not only mitigates the noise but also enables the on-demand retrieval of the transduced signal. Here, we integrate a quantum memory protocol with transduction in a three-level atomic system to demonstrate on-demand retrieval of transduced signals. Due to the zero-first-order Zeeman transitions at zero magnetic fields, providing long optical and spin coherence times, and GHz range hyperfine splitting, we use a low-doping concentration $^{171}{\rm Yb}^{3+}$:${\rm Y}_2{\rm SiO}_5$ crystal at 30\,mK temperature. We achieve on-demand transduction assisted by memory with $0.4\ (\text{and }0.3)$ noise photons in the detection window at a storage duration of $460\ (\text{and }620) \, μ\textrm{s}$. To demonstrate the coherent nature of the protocol, we show interference patterns resulting from transduced signals due to varying phase or frequency of the input microwave pulses. Further, multimode transduction capacity is demonstrated, utilizing the spin and optical inhomogeneous broadening. The on-demand capability of the protocol allows synchronizing qubits in a quantum repeater protocol, while multimode capacity increases the entanglement generation rate. To the best of our knowledge, this is the first demonstration of an on-demand microwave-to-optical transducer assisted by memory. △ Less

Submitted 2 May, 2026; originally announced May 2026.

Comments: 22 pages, 19 figures

Revisiting claims of extracranial biophoton detection from the human brain

Authors: Vahid Salari, Vishnu Seshan, Rishabh Rishabh, Daniel Oblak, Christoph Simon

Abstract: Ultraweak photon emission, also referred to as biological autoluminescence or biophoton emission, is the spontaneous emission of extremely low levels of light from a broad range of biological systems. Recent studies have reported that UPE measured extracranially can serve as a potential non-invasive biomarker of brain activity. Here, we show that this interpretation suffers from serious problems.… ▽ More Ultraweak photon emission, also referred to as biological autoluminescence or biophoton emission, is the spontaneous emission of extremely low levels of light from a broad range of biological systems. Recent studies have reported that UPE measured extracranially can serve as a potential non-invasive biomarker of brain activity. Here, we show that this interpretation suffers from serious problems. We show that, when observed under properly dark conditions, the UPE from the head is much weaker than what is reported in certain papers on 'brain UPE' from human heads. We also show that the large signals reported in these studies can be explained by background light contamination. Furthermore, photons with wavelengths < 600 nm are strongly attenuated by scalp and skull tissues, and longer wavelengths fall largely outside the effective spectral sensitivity of the photomultiplier tubes (PMTs) used. As a consequence, even if UPE from the head is detected under properly background-free conditions, it is likely to be dominated by emission from the scalp rather than from the brain, certainly as long as PMTs are used. Our results emphasize the importance of careful experimental design to make genuine progress on this important question. △ Less

Submitted 26 May, 2026; v1 submitted 27 March, 2026; originally announced March 2026.

Comments: 8 pages (single-column), 5 figures

On-Demand Millisecond Storage of Spectro-Temporal Multimode Telecom Photons

Authors: Anuj Sethia, Nasser Gohari Kamel, Daniel Oblak

Abstract: The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extend… ▽ More The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extended storage times and large multimode capacities. In this work, we experimentally demonstrate such a memory operating at telecom wavelength using an Er$^{3+}$:Y$_{2}$SiO$_{5}$ crystal. Using single-photon detectors, we record on-demand storage and recall of weak coherent pulses for up to $1$ ms, exceeding that of previously reported quantum memories based on Er$^{3+}$. The memory exhibits an efficiency of 10.36\% at 300 $μ$s storage time with a signal-to-noise ratio of $10.9$. We further showcase its multimode capacity by storing 20 temporal and 3 spectral modes simultaneously with on-demand and selective recall capabilities, essential for a scalable quantum repeater architecture. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Generalized Deutsch-Jozsa Algorithm for Applications in Data Classification, Logistic Regression, and Quantum Key Distribution

Authors: M. Ghadimi, V. Salari, S. Bakrani, M. Zomorodi, N. Gohari-Kamel, S. Moradi, D. Oblak

Abstract: We present a generalized Deutsch-Jozsa (DJ) quantum algorithm that not only determines both the global type of an unknown Boolean function (constant or balanced) but also determines explicit output values of the function in a single oracle query. Unlike the original DJ algorithm, which identifies only whether a function is constant or balanced, our generalization retrieves actual function output v… ▽ More We present a generalized Deutsch-Jozsa (DJ) quantum algorithm that not only determines both the global type of an unknown Boolean function (constant or balanced) but also determines explicit output values of the function in a single oracle query. Unlike the original DJ algorithm, which identifies only whether a function is constant or balanced, our generalization retrieves actual function output values at the same time with using a Bell state as ancilla. This makes a richer function characterization with minimal queries to have practical quantum advantages, e.g. data classification, logistic regression, and quantum cryptography. △ Less

Submitted 29 November, 2025; originally announced December 2025.

Quantum Optical Techniques for Biomedical Imaging

Authors: Vahid Salari, Yingwen Zhang, Sepideh Ahmadi, Dilip Paneru, Duncan England, Shabir Barzanjeh, Robert Boyd, Ebrahim Karimi, Christoph Simon, Daniel Oblak

Abstract: Quantum imaging is emerging as a transformative approach for biomedical applications, applying nonclassical properties of light, such as entanglement, squeezing, and quantum correlations, to overcome fundamental limits of conventional techniques. These methods promise superior spatial resolution, enhanced signal-to-noise ratios, improved phase sensitivity, and reduced radiation dose, for potential… ▽ More Quantum imaging is emerging as a transformative approach for biomedical applications, applying nonclassical properties of light, such as entanglement, squeezing, and quantum correlations, to overcome fundamental limits of conventional techniques. These methods promise superior spatial resolution, enhanced signal-to-noise ratios, improved phase sensitivity, and reduced radiation dose, for potentially safer and more precise imaging for delicate biological samples. Here, we present an overview of quantum optical biomedical imaging technologies as well as quantum-inspired imaging methods, including quantum optical coherence tomography, quantum optical microscopy, ghost imaging, multi-parameter quantum imaging, and imaging with quantum-grade cameras. We describe the operating principles, biomedical applications, and unique advantages of each approach, along with the specific challenges for their translation into real-life practice. This review aims to guide future research toward advancing quantum imaging from experimental demonstrations to impactful biomedical tools. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 20 pages, 8 figures

Ultra-narrow homogeneous linewidths of erbium-doped silica glass fibers at millikelvin temperatures: magnetic field and temperature dependence

Authors: Farhad Rasekh, Nasser Gohari Kamel, Mahdi Bornadel, Sourabh Kumar, Erhan Saglamyurek, Christoph Simon, Daniel Oblak

Abstract: Erbium-doped solids are promising candidates for fiber-based quantum networks due to their emission wavelength, which aligns with the telecom band over which optical fibers exhibit minimal loss. Among these, erbium-doped silica fiber (EDF) stands out for its availability, ease of use, and seamless integration with existing fiber-optic infrastructure. In this work, using the two-pulse photon-echo (… ▽ More Erbium-doped solids are promising candidates for fiber-based quantum networks due to their emission wavelength, which aligns with the telecom band over which optical fibers exhibit minimal loss. Among these, erbium-doped silica fiber (EDF) stands out for its availability, ease of use, and seamless integration with existing fiber-optic infrastructure. In this work, using the two-pulse photon-echo (2PPE) technique, we measured the homogeneous linewidth of the 4I13/2 <-> 4I15/2 optical transition under varying magnetic fields and temperatures. We observed an effective homogeneous linewidth of approximately 8 kHz at approximately 7mK at an optimal magnetic field of 0.09 T, representing over two orders of magnitude improvement compared to earlier reports measured at T = 700 mK. We also present a comprehensive model for the combined magnetic field and temperature dependency of the effective homogeneous linewidth. Additionally, we employed three-pulse photon-echo (3PPE) measurements to investigate spectral diffusion and decoherence processes, and conclude that Two-Level System (TLS) effects are significantly suppressed at sufficiently low temperatures, below approximately 100 mK. △ Less

Submitted 27 September, 2025; originally announced September 2025.

Erbium-Doped Fibre Quantum Memory for Chip-Integrated Quantum-Dot Single Photons at 980 nm

Authors: Nasser Gohari Kamel, Arsalan Mansourzadeh, Ujjwal Gautam, Vinaya Kumar Kavatamane, Ashutosh Singh, Edith Yeung, David B. Northeast, Paul Barclay, Philip J. Poole, Dan Dalacu, Daniel Oblak

Abstract: The realization of long-distance quantum communication and the envisioned quantum internet relies on coherent hybrid light-matter interfaces connecting quantum light emitters with quantum memory (QM) systems. Unlike probabilistic photon pair sources such as spontaneous parametric down-conversion, deterministic quantum light emitters enable the on-demand production of pure and bright single and ent… ▽ More The realization of long-distance quantum communication and the envisioned quantum internet relies on coherent hybrid light-matter interfaces connecting quantum light emitters with quantum memory (QM) systems. Unlike probabilistic photon pair sources such as spontaneous parametric down-conversion, deterministic quantum light emitters enable the on-demand production of pure and bright single and entangled photons, essential for scalable quantum networks. In this work, we present the first experimental realization of a coherent hybrid light-matter interface between a chip-integrated InAsP/InP nanowire quantum dot (QD) and a solid-state QM based on Er$^{3+}$ ions doped in a glass silica fiber (erbium-doped fiber, EDF). The emission spectrum of the InAsP/InP nanowire QD aligns with the absorption bandwidth of the EDF at 980 nm at cryogenic temperatures, allowing efficient interaction between the two systems. To demonstrate this, we present a spectroscopic characterization of the $^{4}I_{15/2} \leftrightarrow ^{4}I_{11/2}$ optical transition in EDF at 980 nm. Our measurements reveal substantial inhomogeneous broadening of this optical transition and a long spin population lifetime, underscoring EDFs potential for broadband QM implementation. We implement an 8 GHz bandwidth multimode QM based on the Atomic Frequency Comb protocol, enabling the storage and retrieval of 59 weak coherent pulses. Furthermore, we characterize single-photon emission from an InAsP/InP nanowire QD at 980 nm and demonstrate its deterministic storage and recall in the EDF QM. Notably, this is achieved without spectral tuning of the QD emission, demonstrating its direct compatibility with a solid-state QM. △ Less

Submitted 2 August, 2025; originally announced August 2025.

Photonic quantum information with time-bins: Principles and applications

Authors: Ashutosh Singh, Anuj Sethia, Leili Esmaeilifar, Raju Valivarthi, Neil Sinclair, Maria Spiropulu, Daniel Oblak

Abstract: Long-range quantum communication, distributed quantum computing, and sensing applications require robust and reliable ways to encode transmitted quantum information. In this context, time-bin encoding has emerged as a promising candidate due to its resilience to mechanical and thermal perturbations, depolarization from refractive index changes, and birefringence in fiber optic media. Time-bin quan… ▽ More Long-range quantum communication, distributed quantum computing, and sensing applications require robust and reliable ways to encode transmitted quantum information. In this context, time-bin encoding has emerged as a promising candidate due to its resilience to mechanical and thermal perturbations, depolarization from refractive index changes, and birefringence in fiber optic media. Time-bin quantum bits (qubits) can be produced in various ways, and each implementation calls for different considerations regarding design parameters, component compatibility (optical, electrical, electro-optical), and measurement procedures. Here, we provide a comprehensive overview of experimental methods for preparing and characterizing time-bin qubits (TBQs) for quantum communication protocols, with an assessment of their advantages and limitations. We discuss challenges in transmitting TBQs over optical fibers and free-space channels, and methods to overcome them. We also analyze the selection of key time-bin parameters and component requirements across experiments. This leads us to explore the preparation and characterization of time-bin entanglement and examine requirements for interference of time-bins from separate sources. Further, we cover preparation and characterization techniques for high-dimensional time-bin states, namely qudits, and the generation of time-bin entangled qudit pairs. We review time-energy entanglement and key experimental realizations. Finally, we present notable applications of time-bin encoded quantum states, from quantum communication protocols to photonic quantum computation. This work serves as an accessible introduction and a comprehensive review of recent developments. △ Less

Submitted 2 July, 2026; v1 submitted 10 July, 2025; originally announced July 2025.

Comments: Accepted for publication in Physics Reports (review article); 114 pages, 39 figures, and 819 references

Multimode and Random-Access Optical Quantum Memory via Adiabatic Phase Imprinting

Authors: Nasser Gohari Kamel, Sourabh Kumar, Ujjwal Gautam, Erhan Saglamyurek, Vahid Salari, Daniel Oblak

Abstract: A photonic quantum memory capable of simultaneously storing multiple qubits and subsequently recalling any randomly selected subset of the qubits, is essential for large-scale quantum networking and computing. Such functionality, akin to classical Random-Access Memory (RAM), has proven difficult to implement due to the absence of a versatile random-access mechanism and limited multimode capacity i… ▽ More A photonic quantum memory capable of simultaneously storing multiple qubits and subsequently recalling any randomly selected subset of the qubits, is essential for large-scale quantum networking and computing. Such functionality, akin to classical Random-Access Memory (RAM), has proven difficult to implement due to the absence of a versatile random-access mechanism and limited multimode capacity in existing quantum memory protocols. A potential path to developing the quantum analog to RAM is offered by photon-echo protocols in rare-earth ion-doped materials, such as Revival Of Silenced Echo. These can utilize optical rephasing pulses to selectively read-out frequency multiplexed photonic qubits within an inhomogeneously broadened optical transition. However, the conventional non-adiabatic nature of the rephasing pulses requires intense, short-duration pulses, impeding their fidelity and multimode capacity. To address these critical limitations, we introduce an alternate protocol that employs Rapid Adiabatic Passage (RAP) rephasing pulses, to realize quantum memory, which invokes phase-imprints to suppress undesirable echoes. Using the optical transitions of a $^{171}{\rm Yb}^{3+}$:${\rm Y}_2{\rm SiO}_5$ crystal, we demonstrate the storage and retrieval of multiple intricate spectro-temporally photonic modes and achieve optical random access memory across eight distinct spectral modes. This protocol yields greatly enhanced mode-mapping versatility while substantially lowering the required rephasing pulse intensity, providing a more efficient and reliable approach for high-fidelity qubit storage and retrieval. △ Less

Submitted 13 June, 2025; originally announced June 2025.

Comments: 12 pages, 5 figures

Hole burning experiments and modeling in erbium-doped silica glass fibers down to millikelvin temperatures: evidence for ultra-long population storage

Authors: Mahdi Bornadel, Sara Shafiei Alavijeh, Farhad Rasekh, Nasser Gohari Kamel, Faezeh Kimiaee Asadi, Erhan Saglamyurek, Daniel Oblak, Christoph Simon

Abstract: We use spectral hole burning to investigate spin dynamics within the electronic Zeeman sublevels of the ground state of the erbium ions in erbium-doped fibers (EDF). Conducted at ultra-low temperatures and under varying magnetic fields, our study reveals distinct changes in spin relaxation dynamics across different conditions. We identified three decay components at approximately 7 mK, with one ac… ▽ More We use spectral hole burning to investigate spin dynamics within the electronic Zeeman sublevels of the ground state of the erbium ions in erbium-doped fibers (EDF). Conducted at ultra-low temperatures and under varying magnetic fields, our study reveals distinct changes in spin relaxation dynamics across different conditions. We identified three decay components at approximately 7 mK, with one achieving spin lifetimes of over 9 hours under optimal conditions, while two components were observed at higher temperatures. The fairly stable relative weights of the decay components across conditions suggest distinct ion populations contributing to the observed relaxation dynamics. While earlier studies struggled to account for all decay components at higher temperatures, our approach successfully models spin dynamics across all observed decay components, using a consistent set of underlying mechanisms, including spin flip-flop interactions, direct coupling to two-level systems, and Raman-type processes, and distinguishes the decay components by the strengths with which these mechanisms contribute. These results suggest EDFs' potential as a promising candidate for quantum memory applications, with further room for optimization. △ Less

Submitted 6 October, 2025; v1 submitted 20 December, 2024; originally announced December 2024.

Comments: 12 pages, 8 figures. Published in Physical Review Applied 24, 014030 (2025)

Journal ref: Phys. Rev. Applied 24, 014030 (2025)

Estimating the impact of light pollution on quantum communication between QEYSSat and Canadian quantum ground station sites

Authors: Mathew Yastremski, Paul J. Godin, Nouralhoda Bayat, Sungeun Oh, Ziheng Chang, Katanya B. Kuntz, Daniel Oblak, Thomas Jennewein

Abstract: Satellite to ground quantum communication typically operates at night to reduce background signals, however it remains susceptible to noise from light pollution of the night sky. In this study we compare several methodologies for determining whether a Quantum Ground Station (QGS) site is viable for exchanging quantum signals with the upcoming Quantum Encryption and Science Satellite (QEYSSat) miss… ▽ More Satellite to ground quantum communication typically operates at night to reduce background signals, however it remains susceptible to noise from light pollution of the night sky. In this study we compare several methodologies for determining whether a Quantum Ground Station (QGS) site is viable for exchanging quantum signals with the upcoming Quantum Encryption and Science Satellite (QEYSSat) mission. We conducted ground site characterization studies at three locations in Canada: Waterloo, Ontario, Calgary, Alberta, and Priddis, Alberta. Using different methods we estimate the background counts expected to leak into the satellite-ground quantum channel, and determined whether the noise levels could prevent a quantum key transfer. We also investigate how satellite data recorded from the Visible Infrared Imaging Radiometer Suite (VIIRS) can help estimate conditions of a particular site, and find reasonable agreement with the locally recorded data. Our results indicate that the Waterloo, Calgary, and Priddis QGS sites should allow both quantum uplinks and downlinks with QEYSSat, despite their proximity to urban centres. Furthermore, our approach allows the use of satellite borne instrument data (VIIRS) to remotely and efficiently determine the potential of a ground site. △ Less

Submitted 19 December, 2024; originally announced December 2024.

Comments: Submitted to EPJ: Prospects for Space Quantum Research, 20 pages, 12 figures

Optical Investigations of Coherence and Relaxation Dynamics of a Thulium-doped Yttrium Gallium Garnet Crystal at sub-Kelvin Temperatures for Optical Quantum Memory

Authors: Antariksha Das, Mohsen Falamarzi Askarani, Jacob H. Davidson, Neil Sinclair, Joshua A. Slater, Sara Marzban, Daniel Oblak, Charles W. Thiel, Rufus L. Cone, Wolfgang Tittel

Abstract: Rare-earth ion-doped crystals are of great interest for quantum memories, a central component in future quantum repeaters. To assess the promise of 1$\%$ Tm$^{3+}$-doped yttrium gallium garnet (Tm:YGG), we report measurements of optical coherence and energy-level lifetimes of its $^3$H$_6$ $\leftrightarrow$ $^3$H$_4$ transition at a temperature of around 500 mK and various magnetic fields. Using s… ▽ More Rare-earth ion-doped crystals are of great interest for quantum memories, a central component in future quantum repeaters. To assess the promise of 1$\%$ Tm$^{3+}$-doped yttrium gallium garnet (Tm:YGG), we report measurements of optical coherence and energy-level lifetimes of its $^3$H$_6$ $\leftrightarrow$ $^3$H$_4$ transition at a temperature of around 500 mK and various magnetic fields. Using spectral hole burning, we find hyperfine ground-level (Zeeman level) lifetimes of several minutes at magnetic fields of less than 1000 G. We also measure coherence time exceeding one millisecond using two-pulse photon echoes. Three-pulse photon echo and spectral hole burning measurements reveal that due to spectral diffusion, the effective coherence time reduces to a few $μ$s over a timescale of around two hundred seconds. Finally, temporal and frequency-multiplexed storage of optical pulses using the atomic frequency comb protocol is demonstrated. Our results suggest Tm:YGG to be promising for multiplexed photonic quantum memory for quantum repeaters. △ Less

Submitted 12 June, 2024; originally announced June 2024.

Flexible polar encoding for information reconciliation in QKD

Authors: Snehasis Addy, Sabyasachi Dutta, Somnath Panja, Kunal Dey, Reihaneh Safavi-Naini, Daniel Oblak

Abstract: Quantum Key Distribution (QKD) enables two parties to establish a common secret key that is information-theoretically secure by transmitting random bits that are encoded as qubits and sent over a quantum channel, followed by classical information processing steps known as information reconciliation and key extraction. Transmission of information over a quantum channel introduces errors that are ge… ▽ More Quantum Key Distribution (QKD) enables two parties to establish a common secret key that is information-theoretically secure by transmitting random bits that are encoded as qubits and sent over a quantum channel, followed by classical information processing steps known as information reconciliation and key extraction. Transmission of information over a quantum channel introduces errors that are generally considered to be due to the adversary's tempering with the quantum channel and needs to be corrected using classical communication over an (authenticated) public channel. Commonly used error-correcting codes in the context of QKD include cascade codes, low-density parity check (LDPC) codes, and more recently polar codes. In this work, we explore the applicability of designing of a polar code encoder based on a channel reliability sequence. We show that the reliability sequence can be derived and used to design an encoder independent of the choice of decoder. We then implement our design and evaluate its performance against previous implementations of polar code encoders for QKD as well as other typical error-correcting codes. A key advantage of our approach is the modular design which decouples the encoder and decoder design and allows independent optimization of each. Our work leads to more versatile polar code-based error reconciliation in QKD systems that would result in deployment in a broader range of scenarios. △ Less

Submitted 30 November, 2023; originally announced December 2023.

Comments: 23 pages, 8 figures, 1 table

MSC Class: 81P94 ACM Class: H.1.1

Towards a Realistic Model for Cavity-Enhanced Atomic Frequency Comb Quantum Memories

Authors: Shahrzad Taherizadegan, Jacob H. Davidson, Sourabh Kumar, Daniel Oblak, Christoph Simon

Abstract: Atomic frequency comb (AFC) quantum memory is a favorable protocol in long distance quantum communication. Putting the AFC inside an asymmetric optical cavity enhances the storage efficiency but makes the measurement of the comb properties challenging. We develop a theoretical model for cavity-enhanced AFC quantum memory that includes the effects of dispersion, and show a close alignment of the mo… ▽ More Atomic frequency comb (AFC) quantum memory is a favorable protocol in long distance quantum communication. Putting the AFC inside an asymmetric optical cavity enhances the storage efficiency but makes the measurement of the comb properties challenging. We develop a theoretical model for cavity-enhanced AFC quantum memory that includes the effects of dispersion, and show a close alignment of the model with our own experimental results. Providing semi quantitative agreement for estimating the efficiency and a good description of how the efficiency changes as a function of detuning, it also captures certain qualitative features of the experimental reflectivity. For comparison, we show that a theoretical model without dispersion fails dramatically to predict the correct efficiencies. Our model is a step forward to accurately estimating the created comb properties, such as the optical depth inside the cavity, and so being able to make precise predictions of the performance of the prepared cavity-enhanced AFC quantum memory. △ Less

Submitted 11 December, 2023; v1 submitted 19 September, 2023; originally announced September 2023.

Comments: 7 figures, 10 pages

Quantum storage of 1650 modes of single photons at telecom wavelength

Authors: Shi-Hai Wei, Bo Jing, Xue-Ying Zhang, Jin-Yu Liao, Hao Li, Li-Xing You, Zhen Wang, You Wang, Guang-Wei Deng, Hai-Zhi Song, Daniel Oblak, Guang-Can Guo, Qiang Zhou

Abstract: To advance the full potential of quantum networks one should be able to distribute quantum resources over long distances at appreciable rates. As a consequence, all components in the networks need to have large multimode capacity to manipulate photonic quantum states. Towards this end, a multimode photonic quantum memory, especially one operating at telecom wavelength, remains a key challenge. Her… ▽ More To advance the full potential of quantum networks one should be able to distribute quantum resources over long distances at appreciable rates. As a consequence, all components in the networks need to have large multimode capacity to manipulate photonic quantum states. Towards this end, a multimode photonic quantum memory, especially one operating at telecom wavelength, remains a key challenge. Here we demonstrate a spectro-temporally multiplexed quantum memory at 1532 nm. Multimode quantum storage of telecom-band heralded single photons is realized by employing the atomic frequency comb protocol in a 10-m-long cryogenically cooled erbium doped silica fibre. The multiplexing encompasses five spectral channels - each 10 GHz wide - and in each of these up to 330 temporal modes, resulting in the simultaneous storage of 1650 modes of single photons. Our demonstrations open doors for high-rate quantum networks, which are essential for future quantum internet. △ Less

Submitted 8 February, 2023; v1 submitted 1 September, 2022; originally announced September 2022.

Picosecond synchronization system for quantum networks

Authors: Raju Valivarthi, Lautaro Narváez, Samantha I. Davis, Nikolai Lauk, Cristián Peña, Si Xie, Jason P. Allmaras, Andrew D. Beyer, Boris Korzh, Andrew Mueller, Mandy Rominsky, Matthew Shaw, Emma E. Wollman, Panagiotis Spentzouris, Daniel Oblak, Neil Sinclair, Maria Spiropulu

Abstract: The operation of long-distance quantum networks requires photons to be synchronized and must account for length variations of quantum channels. We demonstrate a 200 MHz clock-rate fiber optic-based quantum network using off-the-shelf components combined with custom-made electronics and telecommunication C-band photons. The network is backed by a scalable and fully automated synchronization system… ▽ More The operation of long-distance quantum networks requires photons to be synchronized and must account for length variations of quantum channels. We demonstrate a 200 MHz clock-rate fiber optic-based quantum network using off-the-shelf components combined with custom-made electronics and telecommunication C-band photons. The network is backed by a scalable and fully automated synchronization system with ps-scale timing resolution. Synchronization of the photons is achieved by distributing O-band-wavelength laser pulses between network nodes. Specifically, we distribute photon pairs between three nodes, and measure a reduction of coincidence-to-accidental ratio from 77 to only 42 when the synchronization system is enabled, which permits high-fidelity qubit transmission. Our demonstration sheds light on the role of noise in quantum communication and represents a key step in realizing deployed co-existing classical-quantum networks. △ Less

Submitted 6 March, 2022; originally announced March 2022.

Comments: 7 pages, 7 figures

Towards real-world quantum networks: a review

Authors: Shi-Hai Wei, Bo Jing, Xue-Ying Zhang, Jin-Yu Liao, Chen-Zhi Yuan, Bo-Yu Fan, Chen Lyu, Dian-Li Zhou, You Wang, Guang-Wei Deng, Hai-Zhi Song, Daniel Oblak, Guang-Can Guo, Qiang Zhou

Abstract: Quantum networks play an extremely important role in quantum information science, with application to quantum communication, computation, metrology and fundamental tests. One of the key challenges for implementing a quantum network is to distribute entangled flying qubits to spatially separated nodes, at which quantum interfaces or transducers map the entanglement onto stationary qubits. The stati… ▽ More Quantum networks play an extremely important role in quantum information science, with application to quantum communication, computation, metrology and fundamental tests. One of the key challenges for implementing a quantum network is to distribute entangled flying qubits to spatially separated nodes, at which quantum interfaces or transducers map the entanglement onto stationary qubits. The stationary qubits at the separated nodes constitute quantum memories realized in matter while the flying qubits constitute quantum channels realized in photons. Dedicated efforts around the world for more than twenty years have resulted in both major theoretical and experimental progress towards entangling quantum nodes and ultimately building a global quantum network. Here, we review the development of quantum networks and the experimental progress over the past two decades leading to the current state of the art for generating entanglement of quantum nodes based on various physical systems such as single atoms, cold atomic ensembles, trapped ions, diamonds with Nitrogen-Vacancy centers, solid-state host doped with rare-earth ions, etc. Along the way we discuss the merits and compare the potential of each of these systems towards realizing a quantum network. △ Less

Submitted 13 January, 2022; originally announced January 2022.

Comments: 71 pages, 16 figures, 1 table, accepted by Laser & Photonics Reviews

Journal ref: Laser & Photonics Reviews volume 16, Article number: 2100219 (2022)

Are Brain-Computer Interfaces Feasible with Integrated Photonic Chips?

Authors: Vahid Salari, Serafim Rodrigues, Erhan Saglamyurek, Christoph Simon, Daniel Oblak

Abstract: The present paper examines the viability of a radically novel idea for brain-computer interface (BCI), which could lead to novel technological, experimental and clinical applications. BCIs are computer-based systems that enable either one-way or two-way communication between a living brain and an external machine. BCIs read-out brain signals and transduce them into task commands, which are perform… ▽ More The present paper examines the viability of a radically novel idea for brain-computer interface (BCI), which could lead to novel technological, experimental and clinical applications. BCIs are computer-based systems that enable either one-way or two-way communication between a living brain and an external machine. BCIs read-out brain signals and transduce them into task commands, which are performed by a machine. In closed-loop, the machine can stimulate the brain with appropriate signals. In recent years, it has been shown that there is some ultraweak light emission from neurons within or close to the visible and near-infrared parts of the optical spectrum. Such ultraweak photon emission (UPE) reflects the cellular (and body) oxidative status, and compelling pieces of evidence are beginning to emerge that UPE may well play an informational role in neuronal functions. In fact, several experiments point to a direct correlation between UPE intensity and neural activity, oxidative reactions, EEG activity, cerebral blood flow, cerebral energy metabolism, and release of glutamate. Here, we propose a novel skull implant BCI that uses UPE. We suggest that a photonic integrated chip installed on the interior surface of the skull may enable a new form of extraction of the relevant features from the UPE signals. In the current technology landscape, photonic technologies advance rapidly and poised to overtake many electrical technologies, due to their unique advantages, such as miniaturization, high speed, low thermal effects, and large integration capacity that allow for high yield, volume manufacturing, and lower cost. For our proposed BCI, we make some major conjectures, which need to be experimentally verified, and hence we discuss the controversial parts, feasibility of technology and limitations, and potential impact of this envisaged technology if successfully implemented in the future. △ Less

Submitted 21 November, 2021; originally announced December 2021.

Comments: 17 pages, 7 figures. Submitted to "Frontiers in Neuroscience". Comments are welcome

Topical White Paper: A Case for Quantum Memories in Space

Authors: Mustafa Gündoğan, Thomas Jennewein, Faezeh Kimiaee Asadi, Elisa Da Ros, Erhan Sağlamyürek, Daniel Oblak, Tobias Vogl, Daniel Rieländer, Jasminder Sidhu, Samuele Grandi, Luca Mazzarella, Julius Wallnöfer, Patrick Ledingham, Lindsay LeBlanc, Margherita Mazzera, Makan Mohageg, Janik Wolters, Alexander Ling, Mete Atatüre, Hugues de Riedmatten, Daniel Oi, Christoph Simon, Markus Krutzik

Abstract: It has recently been theoretically shown that Quantum Memories (QM) could enable truly global quantum networking when deployed in space thereby surpassing the limited range of land-based quantum repeaters. Furthermore, QM in space could enable novel protocols and long-range entanglement and teleportation applications suitable for Deep-Space links and extended scenarios for fundamental physics test… ▽ More It has recently been theoretically shown that Quantum Memories (QM) could enable truly global quantum networking when deployed in space thereby surpassing the limited range of land-based quantum repeaters. Furthermore, QM in space could enable novel protocols and long-range entanglement and teleportation applications suitable for Deep-Space links and extended scenarios for fundamental physics tests. In this white paper we will make the case for the importance of deploying QMs to space, and also discuss the major technical milestones and development stages that will need to be considered. △ Less

Submitted 19 November, 2021; v1 submitted 18 November, 2021; originally announced November 2021.

Comments: Toptical white paper submitted to National Academies of Sciences, Engineering and Medicine's Decadal Survey on Biological and Physical Sciences Research in Space 2023-2032

Sample-efficient adaptive calibration of quantum networks using Bayesian optimization

Authors: Cristian L. Cortes, Pascal Lefebvre, Nikolai Lauk, Michael J. Davis, Neil Sinclair, Stephen K. Gray, Daniel Oblak

Abstract: Indistinguishable photons are imperative for advanced quantum communication networks. Indistinguishability is difficult to obtain because of environment-induced photon transformations and loss imparted by communication channels, especially in noisy scenarios. Strategies to mitigate these transformations often require hardware or software overhead that is restrictive (e.g. adding noise), infeasible… ▽ More Indistinguishable photons are imperative for advanced quantum communication networks. Indistinguishability is difficult to obtain because of environment-induced photon transformations and loss imparted by communication channels, especially in noisy scenarios. Strategies to mitigate these transformations often require hardware or software overhead that is restrictive (e.g. adding noise), infeasible (e.g. on a satellite), or time-consuming for deployed networks. Here we propose and develop resource-efficient Bayesian optimization techniques to rapidly and adaptively calibrate the indistinguishability of individual photons for quantum networks using only information derived from their measurement. To experimentally validate our approach, we demonstrate the optimization of Hong-Ou-Mandel interference between two photons -- a central task in quantum networking -- finding rapid, efficient, and reliable convergence towards maximal photon indistinguishability in the presence of high loss and shot noise. We expect our resource-optimized and experimentally friendly methodology will allow fast and reliable calibration of indistinguishable quanta, a necessary task in distributed quantum computing, communications, and sensing, as well as for fundamental investigations. △ Less

Submitted 10 June, 2021; originally announced June 2021.

A long-lived solid-state optical quantum memory for high-rate quantum repeaters

Authors: Mohsen Falamarzi Askarani, Antariksha Das, Jacob H. Davidson, Gustavo C. Amaral, Neil Sinclair, Joshua A. Slater, Sara Marzban, Charles W. Thiel, Rufus L. Cone, Daniel Oblak, Wolfgang Tittel

Abstract: We argue that long optical storage times are required to establish entanglement at high rates over large distances using memory-based quantum repeaters. Triggered by this conclusion, we investigate the $^3$H$_6$ $\leftrightarrow$ $^3$H$_4$ transition at 795.325 nm of Tm:Y$_3$Ga$_5$O$_{12}$ (Tm:YGG). Most importantly, we show that the optical coherence time can reach 1.1 ms, and, using laser pulses… ▽ More We argue that long optical storage times are required to establish entanglement at high rates over large distances using memory-based quantum repeaters. Triggered by this conclusion, we investigate the $^3$H$_6$ $\leftrightarrow$ $^3$H$_4$ transition at 795.325 nm of Tm:Y$_3$Ga$_5$O$_{12}$ (Tm:YGG). Most importantly, we show that the optical coherence time can reach 1.1 ms, and, using laser pulses, we demonstrate optical storage based on the atomic frequency comb protocol up to 100 $μ$s as well as a memory decay time T$_M$ of 13.1 $μ$s. Possibilities of how to narrow the gap between the measured value of T$_m$ and its maximum of 275 $μ$s are discussed. In addition, we demonstrate quantum state storage using members of non-classical photon pairs. Our results show the potential of Tm:YGG for creating quantum memories with long optical storage times, and open the path to building extended quantum networks. △ Less

Submitted 4 June, 2021; originally announced June 2021.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 127, 220502 (2021)

Optical coherence and energy-level properties of a Tm$^{3+}$-doped LiNbO$_{3}$ waveguide at sub-Kelvin temperatures

Authors: Neil Sinclair, Daniel Oblak, Erhan Saglamyurek, Rufus L. Cone, Charles W. Thiel, Wolfgang Tittel

Abstract: We characterize the optical coherence and energy-level properties of the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 0.65 K. Coherence properties are measured with varied temperature, magnetic field, optical excitation power and wavelength, and measurement time-scale. We also investigate nuclear spin-induced hyperfine structu… ▽ More We characterize the optical coherence and energy-level properties of the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 0.65 K. Coherence properties are measured with varied temperature, magnetic field, optical excitation power and wavelength, and measurement time-scale. We also investigate nuclear spin-induced hyperfine structure and population dynamics with varying magnetic field and laser excitation power. Except for accountable differences due to difference Ti$^{4+}$ and Tm$^{3+}$-doping concentrations, we find that the properties of Tm$^{3+}$:Ti$^{4+}$:LiNbO$_{3}$ produced by indiffusion doping are consistent with those of a bulk-doped Tm$^{3+}$:LiNbO$_{3}$ crystal measured under similar conditions. Our results, which complement previous work in a narrower parameter space, support using rare-earth-ions for integrated optical and quantum signal processing. △ Less

Submitted 21 January, 2021; originally announced January 2021.

Comments: 15 pages, 15 figures

Journal ref: Phys. Rev. B 103, 134105 (2021)

Teleportation Systems Towards a Quantum Internet

Authors: Raju Valivarthi, Samantha Davis, Cristian Pena, Si Xie, Nikolai Lauk, Lautaro Narvaez, Jason P. Allmaras, Andrew D. Beyer, Yewon Gim, Meraj Hussein, George Iskander, Hyunseong Linus Kim, Boris Korzh, Andrew Mueller, Mandy Rominsky, Matthew Shaw, Dawn Tang, Emma E. Wollman, Christoph Simon, Panagiotis Spentzouris, Neil Sinclair, Daniel Oblak, Maria Spiropulu

Abstract: Quantum teleportation is essential for many quantum information technologies including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single photon detectors and off-the-shelf optics, we achieve quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of… ▽ More Quantum teleportation is essential for many quantum information technologies including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single photon detectors and off-the-shelf optics, we achieve quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of >=90% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum internet with practical devices. △ Less

Submitted 28 July, 2020; v1 submitted 21 July, 2020; originally announced July 2020.

Comments: 15 pages, 7 Figures ; fixed typos on affiliation of Christoph Simon (Calgary)

Journal ref: PRX Quantum 1, 020317 (2020)

Improved Light-Matter Interaction for Storage of Quantum States of Light in a Thulium-Doped Crystal Cavity

Authors: Jacob H. Davidson, Pascal Lefebvre, Jun Zhang, Daniel Oblak, Wolfgang Tittel

Abstract: We design and implement an atomic frequency comb quantum memory for 793 nm wavelength photons using a monolithic cavity based on a thulium-doped Y$_3$Al$_5$O$_{12}$ (Tm:YAG) crystal. Approximate impedance matching results in the absorption of approximately $90\%$ of input photons and a memory efficiency of (27.5$\pm$ 2.7)% over a 500 MHz bandwidth. The cavity enhancement leads to a significant imp… ▽ More We design and implement an atomic frequency comb quantum memory for 793 nm wavelength photons using a monolithic cavity based on a thulium-doped Y$_3$Al$_5$O$_{12}$ (Tm:YAG) crystal. Approximate impedance matching results in the absorption of approximately $90\%$ of input photons and a memory efficiency of (27.5$\pm$ 2.7)% over a 500 MHz bandwidth. The cavity enhancement leads to a significant improvement over the previous efficiency in Tm-doped crystals using a quantum memory protocol. In turn, this allows us for the first time to store and recall quantum states of light in such a memory. Our results demonstrate progress toward efficient and faithful storage of single photon qubits with large time-bandwidth product and multi-mode capacity for quantum networking. △ Less

Submitted 30 January, 2020; originally announced January 2020.

Journal ref: Phys. Rev. A 101, 042333 (2020)

Persistent atomic frequency comb based on Zeeman sub-levels of an erbium-doped crystal waveguide

Authors: Mohsen Falamarzi Askarani, Thomas Lutz, Marcelli Grimau Puigibert, Neil Sinclair, Daniel Oblak, Wolfgang Tittel

Abstract: Long-lived sub-levels of the electronic ground-state manifold of rare-earth ions in crystals can be used as atomic population reservoirs for photon echo-based quantum memories. We measure the dynamics of the Zeeman sub-levels of erbium ions that are doped into a lithium niobate waveguide, finding population lifetimes at cryogenic temperatures as long as seconds. Then, using these levels, we prepar… ▽ More Long-lived sub-levels of the electronic ground-state manifold of rare-earth ions in crystals can be used as atomic population reservoirs for photon echo-based quantum memories. We measure the dynamics of the Zeeman sub-levels of erbium ions that are doped into a lithium niobate waveguide, finding population lifetimes at cryogenic temperatures as long as seconds. Then, using these levels, we prepare and characterize atomic frequency combs, which can serve as a memory for quantum light at 1532 nm wavelength. The results allow predicting a 0.1\% memory efficiency, mainly limited by unwanted background absorption that we conjecture to be caused by the coupling between two-level systems (TLS) and erbium spins. Hence, while it should be possible to create an AFC-based quantum memory in Er$^{3+}$:Ti$^{3+}$:LiNbO$_3$, improved crystal growth together with optimized AFC preparation will be required to make it suitable for applications in quantum communication. △ Less

Submitted 19 July, 2019; v1 submitted 17 July, 2019; originally announced July 2019.

Comments: 7 pages, 5 figures

Journal ref: JOSA B 37.2 (2020): 352-358

Entanglement and non-locality between disparate solid-state quantum memories mediated by photons

Authors: Marcel. li Grimau Puigibert, Mohsen Falamarzi Askarani, Jacob H. Davidson, Varun B. Verma, Matthew D. Shaw, Sae Woo Nam, Thomas Lutz, Gustavo C. Amaral, Daniel Oblak, Wolfgang Tittel

Abstract: Entangling quantum systems with different characteristics through the exchange of photons is a prerequisite for building future quantum networks. Proving the presence of entanglement between quantum memories for light working at different wavelengths furthers this goal. Here, we report on a series of experiments with a thulium-doped crystal, serving as a quantum memory for 794 nm photons, an erbiu… ▽ More Entangling quantum systems with different characteristics through the exchange of photons is a prerequisite for building future quantum networks. Proving the presence of entanglement between quantum memories for light working at different wavelengths furthers this goal. Here, we report on a series of experiments with a thulium-doped crystal, serving as a quantum memory for 794 nm photons, an erbium-doped fibre, serving as a quantum memory for telecommunication-wavelength photons at 1535 nm, and a source of photon pairs created via spontaneous parametric down-conversion. Characterizing the photons after re-emission from the two memories, we find non-classical correlations with a cross-correlation coefficient of $g^{(2)}_{12} = 53\pm8$; entanglement preserving storage with input-output fidelity of $\mathcal{F}_{IO}\approx93\pm2\%$; and non-locality featuring a violation of the Clauser-Horne-Shimony-Holt Bell-inequality with $S= 2.6\pm0.2$. Our proof-of-principle experiment shows that entanglement persists while propagating through different solid-state quantum memories operating at different wavelengths. △ Less

Submitted 21 May, 2019; v1 submitted 20 May, 2019; originally announced May 2019.

Comments: 3 figures in main-text and 5 figures in Supplemental Material

Journal ref: Phys. Rev. Research 2, 013039 (2020)

Measurement-device-independent quantum key distribution coexisting with classical communication

Authors: Raju Valivarthi, Prathwiraj Umesh, Caleb John, Kimberley A. Owen, Varun B. Verma, Sae Woo Nam, Daniel Oblak, Qiang Zhou, Wolfgang Tittel

Abstract: The possibility for quantum and classical communication to coexist on the same fibre is important for deployment and widespread adoption of quantum key distribution (QKD) and, more generally, a future quantum internet. While coexistence has been demonstrated for different QKD implementations, a comprehensive investigation for measurement-device independent (MDI) QKD -- a recently proposed QKD prot… ▽ More The possibility for quantum and classical communication to coexist on the same fibre is important for deployment and widespread adoption of quantum key distribution (QKD) and, more generally, a future quantum internet. While coexistence has been demonstrated for different QKD implementations, a comprehensive investigation for measurement-device independent (MDI) QKD -- a recently proposed QKD protocol that cannot be broken by quantum hacking that targets vulnerabilities of single-photon detectors -- is still missing. Here we experimentally demonstrate that MDI-QKD can operate simultaneously with at least five 10 Gbps bidirectional classical communication channels operating at around 1550 nm wavelength and over 40 km of spooled fibre, and we project communication rates in excess of 10 THz when moving the quantum channel from the third to the second telecommunication window. The similarity of MDI-QKD with quantum repeaters suggests that classical and generalised quantum networks can co-exist on the same fibre infrastructure. △ Less

Submitted 1 May, 2019; originally announced May 2019.

Comments: 12 pages, 3 figures

Storage and retrieval of heralded telecommunication-wavelength photons using a solid-state waveguide quantum memory

Authors: Mohsen Falamarzi Askarani, Marcel. li Grimau Pugibert, Thomas Lutz, Varun B. Verma, Matthew D. Shaw, Sae Woo Nam, Neil Sinclair, Daniel Oblak, Wolfgang Tittel

Abstract: Large-scale quantum networks will employ telecommunication-wavelength photons to exchange quantum information between remote measurement, storage, and processing nodes via fibre-optic channels. Quantum memories compatible with telecommunication-wavelength photons are a key element towards building such a quantum network. Here, we demonstrate the storage and retrieval of heralded 1532 nm-wavelength… ▽ More Large-scale quantum networks will employ telecommunication-wavelength photons to exchange quantum information between remote measurement, storage, and processing nodes via fibre-optic channels. Quantum memories compatible with telecommunication-wavelength photons are a key element towards building such a quantum network. Here, we demonstrate the storage and retrieval of heralded 1532 nm-wavelength photons using a solid-state waveguide quantum memory. The heralded photons are derived from a photon-pair source that is based on parametric down-conversion, and our quantum memory is based on a 6 GHz-bandwidth atomic frequency comb prepared using an inhomogeneously broadened absorption line of a cryogenically-cooled erbium-doped lithium niobate waveguide. Using persistent spectral hole burning under varying magnetic fields, we determine that the memory is enabled by population transfer into niobium and lithium nuclear spin levels. Despite limited storage time and efficiency, our demonstration represents an important step towards quantum networks that operate in the telecommunication band and the development of on-chip quantum technology using industry-standard crystals. △ Less

Submitted 16 April, 2018; originally announced April 2018.

Comments: 8 pages, 4 figures

Journal ref: Phys. Rev. Applied 11, 054056 (2019)

Entanglement between more than two hundred macroscopic atomic ensembles in a solid

Authors: P. Zarkeshian, C. Deshmukh, N. Sinclair, S. K. Goyal, G. H. Aguilar, P. Lefebvre, M. Grimau Puigibert, V. B. Verma, F. Marsili, M. D. Shaw, S. W. Nam, K. Heshami, D. Oblak, W. Tittel, C. Simon

Abstract: We create a multi-partite entangled state by storing a single photon in a crystal that contains many large atomic ensembles with distinct resonance frequencies. The photon is re-emitted at a well-defined time due to an interference effect analogous to multi-slit diffraction. We derive a lower bound for the number of entangled ensembles based on the contrast of the interference and the single-photo… ▽ More We create a multi-partite entangled state by storing a single photon in a crystal that contains many large atomic ensembles with distinct resonance frequencies. The photon is re-emitted at a well-defined time due to an interference effect analogous to multi-slit diffraction. We derive a lower bound for the number of entangled ensembles based on the contrast of the interference and the single-photon character of the input, and we experimentally demonstrate entanglement between over two hundred ensembles, each containing a billion atoms. In addition, we illustrate the fact that each individual ensemble contains further entanglement. Our results are the first demonstration of entanglement between many macroscopic systems in a solid and open the door to creating even more complex entangled states. △ Less

Submitted 14 March, 2017; originally announced March 2017.

Comments: 10 pages, 8 figures; see also parallel submission by Frowis et al

Journal ref: Nature Communications 8, 906 (2017)

Heralded single photons based on spectral multiplexing and feed-forward control

Authors: M. Grimau Puigibert, G. H. Aguilar, Q. Zhou, F. Marsili, M. D. Shaw, V. B. Verma, S. W. Nam, D. Oblak, W. Tittel

Abstract: We propose and experimentally demonstrate a novel approach to a heralded single photon source based on spectral multiplexing (SMUX) and feed-forward-based spectral manipulation of photons created by means of spontaneous parametric down-conversion in a periodically-poled LiNbO3 crystal. As a proof-of-principle, we show that our 3-mode SMUX increases the heralded single-photon rate compared to that… ▽ More We propose and experimentally demonstrate a novel approach to a heralded single photon source based on spectral multiplexing (SMUX) and feed-forward-based spectral manipulation of photons created by means of spontaneous parametric down-conversion in a periodically-poled LiNbO3 crystal. As a proof-of-principle, we show that our 3-mode SMUX increases the heralded single-photon rate compared to that of the individual modes without compromising the quality of the emitted single-photons. We project that by adding further modes, our approach can lead to a deterministic SPS. △ Less

Submitted 6 March, 2017; originally announced March 2017.

Comments: Main text and supplementary material

Journal ref: Phys. Rev. Lett. 119, 083601 (2017)

A cost-effective measurement-device-independent quantum key distribution system for quantum networks

Authors: Raju Valivarthi, Qiang Zhou, Caleb John, Francesco Marsili, Varun B. Verma, Matthew D. Shaw, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: We experimentally realize a measurement-device-independent quantum key distribution (MDI-QKD) system based on cost-effective and commercially available hardware such as distributed feedback (DFB) lasers and field-programmable gate arrays (FPGA) that enable time-bin qubit preparation and time-tagging, and active feedback systems that allow for compensation of time-varying properties of photons afte… ▽ More We experimentally realize a measurement-device-independent quantum key distribution (MDI-QKD) system based on cost-effective and commercially available hardware such as distributed feedback (DFB) lasers and field-programmable gate arrays (FPGA) that enable time-bin qubit preparation and time-tagging, and active feedback systems that allow for compensation of time-varying properties of photons after transmission through deployed fibre. We examine the performance of our system, and conclude that its design does not compromise performance. Our demonstration paves the way for MDI-QKD-based quantum networks in star-type topology that extend over more than 100 km distance. △ Less

Submitted 16 February, 2017; originally announced February 2017.

Comments: 6 pages, 3 figures

Quantum teleportation across a metropolitan fibre network

Authors: Raju Valivarthi, Marcel. li Grimau Puigibert, Qiang Zhou, Gabriel H. Aguilar, Varun B. Verma, Francesco Marsili, Matthew D. Shaw, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: If a photon interacts with a member of an entangled photon pair via a so-called Bell-state measurement (BSM), its state is teleported over principally arbitrary distances onto the second member of the pair. Starting in 1997, this puzzling prediction of quantum mechanics has been demonstrated many times; however, with one very recent exception, only the photon that received the teleported state, if… ▽ More If a photon interacts with a member of an entangled photon pair via a so-called Bell-state measurement (BSM), its state is teleported over principally arbitrary distances onto the second member of the pair. Starting in 1997, this puzzling prediction of quantum mechanics has been demonstrated many times; however, with one very recent exception, only the photon that received the teleported state, if any, travelled far while the photons partaking in the BSM were always measured closely to where they were created. Here, using the Calgary fibre network, we report quantum teleportation from a telecommunication-wavelength photon, interacting with another telecommunication photon after both have travelled over several kilometres in bee-line, onto a photon at 795~nm wavelength. This improves the distance over which teleportation takes place from 818~m to 6.2~km. Our demonstration establishes an important requirement for quantum repeater-based communications and constitutes a milestone on the path to a global quantum Internet. △ Less

Submitted 27 May, 2016; originally announced May 2016.

Properties of a rare-earth-ion-doped waveguide at sub-Kelvin temperatures for quantum signal processing

Authors: Neil Sinclair, Daniel Oblak, Charles W. Thiel, Rufus L. Cone, Wolfgang Tittel

Abstract: We characterize the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes -- up to 117 $μ$s and 2.5 hours, respectively -- exceed those at 3 K at least ten-fold, and are equivalent to those observed in a bulk Tm$^{3+}$:LiNbO$_{3}$ crystal under similar conditions. We also find a tran… ▽ More We characterize the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes -- up to 117 $μ$s and 2.5 hours, respectively -- exceed those at 3 K at least ten-fold, and are equivalent to those observed in a bulk Tm$^{3+}$:LiNbO$_{3}$ crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5 GHz-bandwidth atomic frequency comb of finesse $>$2 on a vanishing background. These results demonstrate the suitability of rare-earth-doped waveguides created using industry-standard Ti-indiffusion in LiNbO$_3$ for on-chip quantum applications. △ Less

Submitted 17 March, 2017; v1 submitted 8 May, 2016; originally announced May 2016.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 118, 100504 (2017)

A multiplexed light-matter interface for fibre-based quantum networks

Authors: Erhan Saglamyurek, Marcel. li Grimau Puigibert, Qiang Zhou, Lambert Giner, Francesco Marsili, Varun B. Verma, Sae Woo Nam, Lee Oesterling, David Nippa, Daniel Oblak, Wolfgang Tittel

Abstract: Processing and distributing quantum information using photons through fibre-optic or free-space links is essential for building future quantum networks. The scalability needed for such networks can be achieved by employing photonic quantum states that are multiplexed into time and/or frequency, and light-matter interfaces that are able to store and process such states with large time-bandwidth pro… ▽ More Processing and distributing quantum information using photons through fibre-optic or free-space links is essential for building future quantum networks. The scalability needed for such networks can be achieved by employing photonic quantum states that are multiplexed into time and/or frequency, and light-matter interfaces that are able to store and process such states with large time-bandwidth product and multimode capacities. Despite important progress in developing such devices, the demonstration of these capabilities using non-classical light remains challenging. Employing the atomic frequency comb quantum memory protocol in a cryogenically cooled erbium-doped optical fibre, we report the quantum storage of heralded single photons at a telecom-wavelength (1.53 μm) with a time-bandwidth product approaching 800. Furthermore we demonstrate frequency-multimode storage as well as memory-based spectral-temporal photon manipulation. Notably, our demonstrations rely on fully integrated quantum technologies operating at telecommunication wavelengths, i.e. a fibre-pigtailed nonlinear waveguide for the generation of heralded single photons, an erbium-doped fibre for photon storage and manipulation, and fibre interfaced superconducting nanowire devices for efficient single photon detection. With improved storage efficiency, our light-matter interface may become a useful tool in future quantum networks. △ Less

Submitted 26 November, 2015; v1 submitted 4 November, 2015; originally announced November 2015.

Cross-phase modulation of a probe stored in a waveguide for non-destructive detection of photonic qubits

Authors: Neil Sinclair, Khabat Heshami, Chetan Deshmukh, Daniel Oblak, Christoph Simon, Wolfgang Tittel

Abstract: Non-destructive detection of photonic qubits is an enabling technology for quantum information processing and quantum communication. For practical applications such as quantum repeaters and networks, it is desirable to implement such detection in a way that allows some form of multiplexing as well as easy integration with other components such as solid-state quantum memories. Here we propose an ap… ▽ More Non-destructive detection of photonic qubits is an enabling technology for quantum information processing and quantum communication. For practical applications such as quantum repeaters and networks, it is desirable to implement such detection in a way that allows some form of multiplexing as well as easy integration with other components such as solid-state quantum memories. Here we propose an approach to non-destructive photonic qubit detection that promises to have all the mentioned features. Mediated by an impurity-doped crystal, a signal photon in an arbitrary time-bin qubit state modulates the phase of an intense probe pulse that is stored during the interaction. Using a thulium-doped waveguide in LiNbO$_3$, we perform a proof-of-principle experiment with macroscopic signal pulses, demonstrating the expected cross-phase modulation as well as the ability to preserve the coherence between temporal modes. Our findings open the path to a new key component of quantum photonics based on rare-earth-ion doped crystals. △ Less

Submitted 5 October, 2015; originally announced October 2015.

Comments: 6+5 pages, 4 figures

Journal ref: Nature Communications 7, 13454 (2016)

A telecom-wavelength atomic quantum memory in optical fiber for heralded polarization qubits

Authors: Jeongwan Jin, Erhan Saglamyurek, Marcel. li Grimau Puigibert, Varun B. Verma, Francesco Marsili, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this p… ▽ More Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this platform, including sources of entangled photons, efficient single photon detectors, and on-chip quantum circuits, a missing element has been atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of a telecom-wavelength photon. Here we demonstrate the quantum storage and retrieval of polarization states of heralded single-photons at telecom-wavelength by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing. △ Less

Submitted 14 June, 2015; originally announced June 2015.

Comments: The first two authors contributed equally to this work

Journal ref: Phys. Rev. Lett. 115, 140501 (2015)

Entanglement swapping with quantum-memory-compatible photons

Authors: Jeongwan Jin, Marcel. li Grimau Puigibert, Lambert Giner, Joshua A. Slater, Michael R. E. Lamont, Varun B. Verma, M. D. Shaw, Francesco Marsili, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: We report entanglement swapping with time-bin entangled photon pairs, each constituted of a 795 nm photon and a 1533 nm photon, that are created via spontaneous parametric down conversion in a non-linear crystal. After projecting the two 1533 nm photons onto a Bell state, entanglement between the two 795 nm photons is verified by means of quantum state tomography. As an important feature, the wave… ▽ More We report entanglement swapping with time-bin entangled photon pairs, each constituted of a 795 nm photon and a 1533 nm photon, that are created via spontaneous parametric down conversion in a non-linear crystal. After projecting the two 1533 nm photons onto a Bell state, entanglement between the two 795 nm photons is verified by means of quantum state tomography. As an important feature, the wavelength and bandwidth of the 795 nm photons is compatible with Tm:LiNbO3-based quantum memories, making our experiment an important step towards the realization of a quantum repeater. △ Less

Submitted 11 June, 2015; originally announced June 2015.

Comments: Accepted in Phys. Rev. A

Journal ref: Phys. Rev. A 92, 012329 (2015)

Measurement-device-independent quantum key distribution: from idea towards application

Authors: Raju Valivarthi, Itzel Lucio-Martinez, Philip Chan, Allison Rubenok, Caleb John, Daniel Korchinski, Cooper Duffin, Francesco Marsili, Varun Verma, Mathew D. Shaw, Jeffrey A. Stern, Sae Woo Nam, Daniel Oblak, Qiang Zhou, Joshua A. Slater, Wolfgang Tittel

Abstract: We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more… ▽ More We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more than 600 bits of secret key per second (not considering finite key effects) over a 16 dB loss channel. This corresponds to 300 km and 80 km of standard telecommunication fiber, respectively. We also demonstrate that the integration of our QKD system into FPGA-based hardware (instead of state-of-the-art arbitrary waveform generators) does not impact on its performance. Our investigation allows us to acquire an improved understanding of the trade-offs between complexity, cost and system performance, which is required for future customization of MDI-QKD. Given that our system can be operated outside the laboratory over deployed fiber, we conclude that MDI-QKD is a promising approach to information-theoretic secure key distribution. △ Less

Submitted 28 January, 2015; originally announced January 2015.

Comments: 10 pages, 5 figures

Journal ref: Journal of Modern Optics 62, 1141-1150 (2015)

Efficient Bell state analyzer for time-bin qubits with fast-recovery WSi superconducting single photon detectors

Authors: Raju Valivarthi, Itzel Lucio-Martinez, Allison Rubenok, Philip Chan, Francesco Marsili, Varun B. Verma, Matthew D. Shaw, J. A. Stern, Joshua A. Slater, Daniel Oblak, Sae Woo Nam, Wolfgang Tittel

Abstract: We experimentally demonstrate a high-efficiency Bell state measurement for time-bin qubits that employs two superconducting nanowire single-photon detectors with short dead-times, allowing projections onto two Bell states, |Psi>- and |Psi+>. Compared to previous implementations for time-bin qubits, this yields an increase in the efficiency of Bell state analysis by a factor of thirty. We experimentally demonstrate a high-efficiency Bell state measurement for time-bin qubits that employs two superconducting nanowire single-photon detectors with short dead-times, allowing projections onto two Bell states, |Psi>- and |Psi+>. Compared to previous implementations for time-bin qubits, this yields an increase in the efficiency of Bell state analysis by a factor of thirty. △ Less

Submitted 21 October, 2014; v1 submitted 17 October, 2014; originally announced October 2014.

Journal ref: Optics Express, Vol. 22, Issue 20, pp. 24497-24506 (2014)

Quantum storage of entangled telecom-wavelength photons in an erbium-doped optical fibre

Authors: Erhan Saglamyurek, Jeongwan Jin, Varun B. Verma, Matthew D. Shaw, Francesco Marsili, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: The realization of a future quantum Internet requires processing and storing quantum information at local nodes, and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom… ▽ More The realization of a future quantum Internet requires processing and storing quantum information at local nodes, and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom fibre infrastructure, nor a fibre-based implementation of a quantum memory has been reported. Here we demonstrate the storage and faithful recall of the state of a 1532 nm wavelength photon, entangled with a 795 nm photon, in an ensemble of cryogenically cooled erbium ions doped into a 20 meter-long silicate fibre using a photon-echo quantum memory protocol. Despite its currently limited efficiency and storage time, our broadband light-matter interface brings fibre-based quantum networks one step closer to reality. Furthermore, it facilitates novel tests of light-matter interaction and collective atomic effects in unconventional materials. △ Less

Submitted 13 January, 2015; v1 submitted 2 September, 2014; originally announced September 2014.

Comments: 6 pages, 3 Figures + Supplementary Information. The problem with the order of the references is fixed. appears in Nature Photonics (2015)

Journal ref: Nature Photonics 9, 83-87, 2015

An integrated processor for photonic quantum states using a broadband light-matter interface

Authors: Erhan Saglamyurek, Neil Sinclair, Joshua A. Slater, Khabat Heshami, Daniel Oblak, Wolfgang Tittel

Abstract: Faithful storage and coherent manipulation of quantum optical pulses are key for long distance quantum communications and quantum computing. Combining these functions in a light-matter interface that can be integrated on-chip with other photonic quantum technologies, e.g. sources of entangled photons, is an important step towards these applications. To date there have only been a few demonstration… ▽ More Faithful storage and coherent manipulation of quantum optical pulses are key for long distance quantum communications and quantum computing. Combining these functions in a light-matter interface that can be integrated on-chip with other photonic quantum technologies, e.g. sources of entangled photons, is an important step towards these applications. To date there have only been a few demonstrations of coherent pulse manipulation utilizing optical storage devices compatible with quantum states, and that only in atomic gas media (making integration difficult) and with limited capabilities. Here we describe how a broadband waveguide quantum memory based on the Atomic Frequency Comb (AFC) protocol can be used as a programmable processor for essentially arbitrary spectral and temporal manipulations of individual quantum optical pulses. Using weak coherent optical pulses at the few photon level, we experimentally demonstrate sequencing, time-to-frequency multiplexing and demultiplexing, splitting, interfering, temporal and spectral filtering, compressing and stretching as well as selective delaying. Our integrated light-matter interface offers high-rate, robust and easily configurable manipulation of quantum optical pulses and brings fully practical optical quantum devices one step closer to reality. Furthermore, as the AFC protocol is suitable for storage of intense light pulses, our processor may also find applications in classical communications. △ Less

Submitted 24 April, 2014; v1 submitted 3 February, 2014; originally announced February 2014.

Comments: Revised version including a quantitative treatment of the compression and stretching techniques, 22 pages, 12 figures

Journal ref: New J. Phys. 16 065019 (2014)

Spectral multiplexing for scalable quantum photonics using an atomic frequency comb quantum memory and feed-forward control

Authors: Neil Sinclair, Erhan Saglamyurek, Hassan Mallahzadeh, Joshua A. Slater, Mathew George, Raimund Ricken, Morgan P. Hedges, Daniel Oblak, Christoph Simon, Wolfgang Sohler, Wolfgang Tittel

Abstract: Future multi-photon applications of quantum optics and quantum information science require quantum memories that simultaneously store many photon states, each encoded into a different optical mode, and enable one to select the mapping between any input and a specific retrieved mode during storage. Here we show, with the example of a quantum repeater, how to employ spectrally-multiplexed states and… ▽ More Future multi-photon applications of quantum optics and quantum information science require quantum memories that simultaneously store many photon states, each encoded into a different optical mode, and enable one to select the mapping between any input and a specific retrieved mode during storage. Here we show, with the example of a quantum repeater, how to employ spectrally-multiplexed states and memories with fixed storage times that allow such mapping between spectral modes. Furthermore, using a Ti:Tm:LiNbO3 waveguide cooled to 3 Kelvin, a phase modulator, and a spectral filter, we demonstrate storage followed by the required feed-forward-controlled frequency manipulation with time-bin qubits encoded into up to 26 multiplexed spectral modes and 97% fidelity. △ Less

Submitted 18 July, 2014; v1 submitted 12 September, 2013; originally announced September 2013.

Journal ref: Phys. Rev. Lett. 113, 053603 (2014)

Two-photon interference of weak coherent laser pulses recalled from separate solid-state quantum memories

Authors: Jeongwan Jin, Joshua A. Slater, Erhan Saglamyurek, Neil Sinclair, Mathew George, Raimund Ricken, Daniel Oblak, Wolfgang Sohler, Wolfgang Tittel

Abstract: Quantum memories for light, which allow the reversible transfer of quantum states between light and matter, are central to the development of quantum repeaters, quantum networks, and linear optics quantum computing. Significant progress has been reported in recent years, including the faithful transfer of quantum information from photons in pure and entangled qubit states. However, none of these d… ▽ More Quantum memories for light, which allow the reversible transfer of quantum states between light and matter, are central to the development of quantum repeaters, quantum networks, and linear optics quantum computing. Significant progress has been reported in recent years, including the faithful transfer of quantum information from photons in pure and entangled qubit states. However, none of these demonstrations confirm that photons stored in and recalled from quantum memories remain suitable for two-photon interference measurements, such as C-NOT gates and Bell-state measurements, which constitute another key ingredient for all aforementioned applications of quantum information processing. Using pairs of weak laser pulses, each containing less than one photon on average, we demonstrate two-photon interference as well as a Bell-state measurement after either none, one, or both pulses have been reversibly mapped to separate thulium-doped titanium-indiffused lithium niobate (Ti:Tm:LiNbO3) waveguides. As the interference is always near the theoretical maximum, we conclude that our solid-state quantum memories, in addition to faithfully mapping quantum information, also preserves the entire photonic wavefunction. Hence, we demonstrate that our memories are generally suitable for use in advanced applications of quantum information processing that require two-photon interference. △ Less

Submitted 8 February, 2013; originally announced February 2013.

Journal ref: Nature Communications 4, 2386 (2013)

Towards quantum state tomography of a single polariton state of an atomic ensemble

Authors: S. L. Christensen, J. B. Béguin, H. L. Sørensen, E. Bookjans, D. Oblak, J. H. Müller, J. Appel, E. S. Polzik

Abstract: We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward scattered photon. The state is subsequently characterized by atomic state tomography performed using strong dispersive light-atoms interaction… ▽ More We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward scattered photon. The state is subsequently characterized by atomic state tomography performed using strong dispersive light-atoms interaction followed by a homodyne measurement on the transmitted light. The proposal is backed by preliminary experimental results showing projection noise limited sensitivity and a simulation demonstrating the feasibility of the proposed method for detection of a non-classical and non-Gaussian state of the mesoscopic atomic ensemble. This work represents the first attempt of hybrid discrete-continuous variable quantum state processing with atomic ensembles. △ Less

Submitted 30 October, 2012; v1 submitted 7 August, 2012; originally announced August 2012.

Journal ref: 2013 New J. Phys. 15 015002

Conditional detection of pure quantum states of light after storage in a waveguide

Authors: Erhan Saglamyurek, Neil Sinclair, Jeongwan Jin, Joshua A. Slater, Daniel Oblak, Félix Bussières, Mathew George, Raimund Ricken, Wolfgang Sohler, Wolfgang Tittel

Abstract: Conditional detection is an important tool to extract weak signals from a noisy background and is closely linked to heralding, which is an essential component of protocols for long distance quantum communication and distributed quantum information processing in quantum networks. Here we demonstrate the conditional detection of time-bin qubits after storage in and retrieval from a photon-echo based… ▽ More Conditional detection is an important tool to extract weak signals from a noisy background and is closely linked to heralding, which is an essential component of protocols for long distance quantum communication and distributed quantum information processing in quantum networks. Here we demonstrate the conditional detection of time-bin qubits after storage in and retrieval from a photon-echo based waveguide quantum memory. Each qubit is encoded into one member of a photon-pair produced via spontaneous parametric down conversion, and the conditioning is achieved by the detection of the other member of the pair. Performing projection measurements with the stored and retrieved photons onto different bases we obtain an average storage fidelity of 0.885 \pm 0.020, which exceeds the relevant classical bounds and shows the suitability of our integrated light-matter interface for future applications of quantum information processing. △ Less

Submitted 2 November, 2011; originally announced November 2011.

Comments: 4 pages, 4 figures

Journal ref: Phys. Rev. Lett. 108, 083602 (2012)

Broadband waveguide quantum memory for entangled photons

Authors: Erhan Saglamyurek, Neil Sinclair, Jeongwan Jin, Joshua A. Slater, Daniel Oblak, Felix Bussieres, Mathew George, Raimund Ricken, Wolfgang Sohler, Wolfgang Tittel

Abstract: The reversible transfer of quantum states of light in and out of matter constitutes an important building block for future applications of quantum communication: it allows synchronizing quantum information, and enables one to build quantum repeaters and quantum networks. Much effort has been devoted worldwide over the past years to develop memories suitable for the storage of quantum states. Of ce… ▽ More The reversible transfer of quantum states of light in and out of matter constitutes an important building block for future applications of quantum communication: it allows synchronizing quantum information, and enables one to build quantum repeaters and quantum networks. Much effort has been devoted worldwide over the past years to develop memories suitable for the storage of quantum states. Of central importance to this task is the preservation of entanglement, a quantum mechanical phenomenon whose counter intuitive properties have occupied philosophers, physicists and computer scientists since the early days of quantum physics. Here we report, for the first time, the reversible transfer of photon-photon entanglement into entanglement between a photon and collective atomic excitation in a solid-state device. Towards this end, we employ a thulium-doped lithium niobate waveguide in conjunction with a photon-echo quantum memory protocol, and increase the spectral acceptance from the current maximum of 100 MHz to 5 GHz. The entanglement-preserving nature of our storage device is assessed by comparing the amount of entanglement contained in the detected photon pairs before and after the reversible transfer, showing, within statistical error, a perfect mapping process. Our integrated, broadband quantum memory complements the family of robust, integrated lithium niobate devices. It renders frequency matching of light with matter interfaces in advanced applications of quantum communication trivial and institutes several key properties in the quest to unleash the full potential of quantum communication. △ Less

Submitted 6 September, 2010; v1 submitted 2 September, 2010; originally announced September 2010.

Comments: 12 pages, 3 figures; added reference

Journal ref: Nature 469, 512-515 (2011)

Entanglement-assisted atomic clock beyond the projection noise limit

Authors: Anne Louchet-Chauvet, Jürgen Appel, Jelmer J. Renema, Daniel Oblak, Niels Kjærgaard, Eugene S. Polzik

Abstract: We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 10^5 cold cesium atoms, and for the first time operate an atomic clock improved by spin squeezing beyond the projection noise limit in a proof-of-principle experiment. For a clock-interrogation time of 10 μ\s the experiments show an improvement of 1.1 dB in the signal-to-noise rat… ▽ More We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 10^5 cold cesium atoms, and for the first time operate an atomic clock improved by spin squeezing beyond the projection noise limit in a proof-of-principle experiment. For a clock-interrogation time of 10 μ\s the experiments show an improvement of 1.1 dB in the signal-to-noise ratio, compared to the atomic projection noise limit. △ Less

Submitted 21 March, 2010; v1 submitted 19 December, 2009; originally announced December 2009.

Journal ref: New J. Phys. 12 065032, 2010

Squeezing of Atomic Quantum Projection Noise

Authors: Patrick J. Windpassinger, Daniel Oblak, Ulrich B. Hoff, Anne Louchet, Jurgen Appel, Niels Kjaergaard, Eugene S. Polzik

Abstract: We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we conside… ▽ More We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we consider a dual probe scheme which benefits from a cancelation of classical common mode noise sources such that quantum fluctuations from light and atoms are the main contributions to the detected signal. △ Less

Submitted 14 June, 2009; originally announced June 2009.

Comments: Submitted to Journal of Modern Optics

Journal ref: J. Mod. Opt. 56, 1993 (2009)

Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit

Authors: J. Appel, P. J. Windpassinger, D. Oblak, U. B. Hoff, N. Kjaergaard, E. S. Polzik

Abstract: Squeezing of quantum fluctuations by means of entanglement is a well recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between two-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement f… ▽ More Squeezing of quantum fluctuations by means of entanglement is a well recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between two-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for ~ 10^5 cold cesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A two-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared to a single color QND measurement. △ Less

Submitted 28 May, 2009; v1 submitted 20 October, 2008; originally announced October 2008.

Comments: 6 pages+suppl, PNAS format

Journal ref: PNAS (7/2009) vol. 106 no. 27 10960-10965

Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements

Authors: M. Saffman, D. Oblak, J. Appel, E. S. Polzik

Abstract: We analyze the creation of spin squeezed atomic ensembles by simultaneous dispersive interactions with several optical frequencies. A judicious choice of optical parameters enables optimization of an interferometric detection scheme that suppresses inhomogeneous light shifts and keeps the interferometer operating in a balanced mode that minimizes technical noise. We show that when the atoms inte… ▽ More We analyze the creation of spin squeezed atomic ensembles by simultaneous dispersive interactions with several optical frequencies. A judicious choice of optical parameters enables optimization of an interferometric detection scheme that suppresses inhomogeneous light shifts and keeps the interferometer operating in a balanced mode that minimizes technical noise. We show that when the atoms interact with two-frequency light tuned to cycling transitions the degree of spin squeezing $ξ^2$ scales as $ξ^2\sim 1/d$ where $d$ is the resonant optical depth of the ensemble. In real alkali atoms there are loss channels and the scaling may be closer to $ξ^2\sim 1/\sqrt d.$ Nevertheless the use of two-frequencies provides a significant improvement in the degree of squeezing attainable as we show by quantitative analysis of non-resonant probing on the Cs D1 line. Two alternative configurations are analyzed: a Mach-Zehnder interferometer that uses spatial interference, and an interaction with multi-frequency amplitude modulated light that does not require a spatial interferometer. △ Less

Submitted 14 May, 2009; v1 submitted 4 August, 2008; originally announced August 2008.

Comments: 7 figures

Journal ref: Phys. Rev. A 79, 023831 (2009)