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Absence of Charge Offset Drift in a Transmon Qubit
Authors:
Adria Rospars,
Hector Hutin,
Yannick Seis,
Cristóbal Lledó,
Réouven Assouly,
Romain Cazali,
Rémy Dassonneville,
Ambroise Peugeot,
Alexandre Blais,
Audrey Bienfait,
Benjamin Huard
Abstract:
Superconducting quantum circuits are sensitive to their electrostatic environment: uncontrolled charges accumulating on the electrodes of a Josephson junction shift the energy levels of a qubit, perturbing its operation and restricting their design. This effect is captured by a single parameter - the charge offset - whose slow, unpredictable drift has proven difficult to eliminate in practice. Her…
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Superconducting quantum circuits are sensitive to their electrostatic environment: uncontrolled charges accumulating on the electrodes of a Josephson junction shift the energy levels of a qubit, perturbing its operation and restricting their design. This effect is captured by a single parameter - the charge offset - whose slow, unpredictable drift has proven difficult to eliminate in practice. Here, we report a tantalum-based transmon qubit in which the charge offset remains pinned at zero over nearly three months of measurements, including two thermal cycles, with no observable compromise to the qubit lifetime. This exceptional stability disappears in later cooldowns, indicating a fragile mechanism at play. We attribute it to the inductance of a thin superconducting layer inadvertently formed in parallel with the Josephson junction during fabrication. X-ray surface spectroscopy suggests this layer arises from an incomplete wet-etch of tantalum on sapphire. Deliberately engineering such a layer offers a route to eliminating charge-offset drift in superconducting circuits more broadly.
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Submitted 12 March, 2026;
originally announced March 2026.
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Observation and mitigation of microwave echoes from dielectric defects in Josephson traveling wave amplifiers
Authors:
Matteo Boselli,
Joel Grebel,
Ambroise Peugeot,
Rémy Dassonneville,
Benjamin Huard,
Audrey Bienfait
Abstract:
Amplifying microwave signals with a noise close to the minimum imposed by quantum mechanics is now routinely performed with superconducting quantum devices. In particular, Josephson-based Traveling Wave Parametric Amplifiers (JTWPA) have shown record bandwidth with added noise close to the quantum limit. In this work, we report the appearance of echo signals emitted by JTWPAs driven by trains of h…
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Amplifying microwave signals with a noise close to the minimum imposed by quantum mechanics is now routinely performed with superconducting quantum devices. In particular, Josephson-based Traveling Wave Parametric Amplifiers (JTWPA) have shown record bandwidth with added noise close to the quantum limit. In this work, we report the appearance of echo signals emitted by JTWPAs driven by trains of high-power pulses exceeding their dynamical range. we explore the case of weak signals generated through high power pulses. By sending a train of such high-power pulses, beyond the 1 dB compression point of such amplifiers, we observe the appearance of echoes, solely due to the JTWPA. These echoes have micro-second coherence and we attribute their origin to microscopic defects in the amplifier dielectric layer. By analyzing the power and the coherence of the echo signal as a function of temperature, we estimate the dielectric loss brought by these defects, and their impact on the JTWPA quantum efficiency. We introduce a mitigation technique (BLAST) to prevent the appearance of these echoes, consisting in an additional high-power tone sent concurrently with each pulse. We demonstrate that it suppresses the spurious defect signals and we recover the typical gain and noise figure within 95% of their low-power values in 300 ns. These results can help to extend the use of JTWPAs in experiments where fast high-power sequences are necessary to generate weak microwave responses from the system under study, and also provide a path towards characterizing in-situ the dielectric losses of these devices.
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Submitted 20 August, 2025; v1 submitted 28 February, 2025;
originally announced March 2025.
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Amplifying microwave pulses with a single qubit engine fueled by quantum measurements
Authors:
Rémy Dassonneville,
Cyril Elouard,
Romain Cazali,
Réouven Assouly,
Audrey Bienfait,
Alexia Auffèves,
Benjamin Huard
Abstract:
Recent progress in manipulating individual quantum systems enables the exploration of engines exploiting non-classical resources. One of the most appealing is the energy provided by the inherent backaction of quantum measurements. While a handful of experiments have investigated the inner dynamics of engines fueled by measurement backaction, powering a task by such an engine is missing. Here we de…
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Recent progress in manipulating individual quantum systems enables the exploration of engines exploiting non-classical resources. One of the most appealing is the energy provided by the inherent backaction of quantum measurements. While a handful of experiments have investigated the inner dynamics of engines fueled by measurement backaction, powering a task by such an engine is missing. Here we demonstrate the amplification of microwave signals by an engine fueled by repeated quantum measurements of a superconducting transmon qubit. Using feedback, the engine acts as a quantum Maxwell demon operating without a hot thermal source. Measuring the gain of this amplification constitutes a direct probing of the work output of the engine, in contrast with inferring the work by measuring the qubit state along its evolution. Observing a good agreement between both work estimation methods, our experiment validates the accuracy of the indirect method. We characterize the long-term stability of the engine as well as its robustness to transmon decoherence, loss and drifts. Our experiment exemplifies the use of energy brought by quantum measurement backaction.
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Submitted 2 February, 2026; v1 submitted 28 January, 2025;
originally announced January 2025.
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Improving magnetic-field resilience of NbTiN planar resonators using a hard-mask fabrication technique
Authors:
Arne Bahr,
Matteo Boselli,
Benjamin Huard,
Audrey Bienfait
Abstract:
High-quality factor microwave resonators operating in a magnetic field are a necessity for some quantum sensing applications and hybrid platforms. Losses in microwave superconducting resonators can have several origins, including microscopic defects, usually known as two-level-systems (TLS). Here, we characterize the magnetic field response of NbTiN resonators patterned on sapphire and observe cle…
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High-quality factor microwave resonators operating in a magnetic field are a necessity for some quantum sensing applications and hybrid platforms. Losses in microwave superconducting resonators can have several origins, including microscopic defects, usually known as two-level-systems (TLS). Here, we characterize the magnetic field response of NbTiN resonators patterned on sapphire and observe clear absorption lines occurring at specific magnetic fields. We identify the spin systems responsible for these features, including a yet unreported spin with $g=1.85$ that we attribute to defects in the NbTiN thin film. We develop mitigation strategies involving namely an aluminum etch mask, resulting in maintaining quality factors above $Q>2 \times 10^5$ in the range $0$-$0.3$ T.
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Submitted 21 December, 2023;
originally announced December 2023.
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Autoparametric resonance extending the bit-flip time of a cat qubit up to 0.3 s
Authors:
Antoine Marquet,
Antoine Essig,
Joachim Cohen,
Nathanaël Cottet,
Anil Murani,
Emanuele Albertinale,
Simon Dupouy,
Audrey Bienfait,
Théau Peronnin,
Sébastien Jezouin,
Raphaël Lescanne,
Benjamin Huard
Abstract:
Cat qubits, for which logical $|0\rangle$ and $|1\rangle$ are coherent states $|\pmα\rangle$ of a harmonic mode, offer a promising route towards quantum error correction. Using dissipation to our advantage so that photon pairs of the harmonic mode are exchanged with single photons of its environment, it is possible to stabilize the logical states and exponentially increase the bit-flip time of the…
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Cat qubits, for which logical $|0\rangle$ and $|1\rangle$ are coherent states $|\pmα\rangle$ of a harmonic mode, offer a promising route towards quantum error correction. Using dissipation to our advantage so that photon pairs of the harmonic mode are exchanged with single photons of its environment, it is possible to stabilize the logical states and exponentially increase the bit-flip time of the cat qubit with the photon number $|α|^2$. Large two-photon dissipation rate $κ_2$ ensures fast qubit manipulation and short error correction cycles, which are instrumental to correct the remaining phase-flip errors in a repetition code of cat qubits. Here we introduce and operate an autoparametric superconducting circuit that couples a mode containing the cat qubit to a lossy mode whose frequency is set at twice that of the cat mode. This passive coupling does not require a parametric pump and reaches a rate $κ_2/2π\approx 2~\mathrm{MHz}$. With such a strong two-photon dissipation, bit-flip errors of the autoparametric cat qubit are prevented for a characteristic time up to 0.3~s with only a mild impact on phase-flip errors. Besides, we illustrate how the phase of a quantum superposition between $|α\rangle$ and $|-α\rangle$ can be arbitrarily changed by driving the harmonic mode while keeping the engineered dissipation active.
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Submitted 28 April, 2024; v1 submitted 13 July, 2023;
originally announced July 2023.
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Topological power pumping in quantum circuits
Authors:
Jacquelin Luneau,
Clément Dutreix,
Quentin Ficheux,
Pierre Delplace,
Benoît Douçot,
Benjamin Huard,
David Carpentier
Abstract:
In this article, we develop a description of topological pumps as slow classical dynamical variables coupled by a quantum system. We discuss the cases of quantum Hall pumps, Thouless pumps, and the more recent Floquet pumps based frequency converters. This last case corresponds to a quantum topological coupling between classical modes described by action-angle variables on which we focus. We propo…
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In this article, we develop a description of topological pumps as slow classical dynamical variables coupled by a quantum system. We discuss the cases of quantum Hall pumps, Thouless pumps, and the more recent Floquet pumps based frequency converters. This last case corresponds to a quantum topological coupling between classical modes described by action-angle variables on which we focus. We propose a realization of such a topological coupler based on a superconducting qutrit suitably driven by three modulated drives. A detailed experimental protocol allowing to measure the quantized topological power transfer between the different modes of a superconducting circuit is discussed.
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Submitted 3 March, 2022; v1 submitted 27 September, 2021;
originally announced September 2021.
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Number-resolved photocounter for propagating microwave mode
Authors:
Rémy Dassonneville,
Réouven Assouly,
Théau Peronnin,
Pierre Rouchon,
Benjamin Huard
Abstract:
Detectors of propagating microwave photons have recently been realized using superconducting circuits. However a number-resolved photocounter is still missing. In this letter, we demonstrate a single-shot counter for propagating microwave photons that can resolve up to $3$ photons. It is based on a pumped Josephson Ring Modulator that can catch an arbitrary propagating mode by frequency conversion…
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Detectors of propagating microwave photons have recently been realized using superconducting circuits. However a number-resolved photocounter is still missing. In this letter, we demonstrate a single-shot counter for propagating microwave photons that can resolve up to $3$ photons. It is based on a pumped Josephson Ring Modulator that can catch an arbitrary propagating mode by frequency conversion and store its quantum state in a stationary memory mode. A transmon qubit then counts the number of photons in the memory mode using a series of binary questions. Using measurement based feedback, the number of questions is minimal and scales logarithmically with the maximal number of photons. The detector features a detection efficiency of $0.96 \pm 0.04$, and a dark count probability of $0.030 \pm 0.002$ for an average dead time of $4.5~\mathrm{μs}$. To maximize its performance, the device is first used as an \emph{in situ} waveform detector from which an optimal pump is computed and applied. Depending on the number of incoming photons, the detector succeeds with a probability that ranges from $(54 \pm 2)\%$ to $99\%$.
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Submitted 15 October, 2020; v1 submitted 10 April, 2020;
originally announced April 2020.
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Multiplexed photon number measurement
Authors:
Antoine Essig,
Quentin Ficheux,
Théau Peronnin,
Nathanaël Cottet,
Raphaël Lescanne,
Alain Sarlette,
Pierre Rouchon,
Zaki Leghtas,
Benjamin Huard
Abstract:
When a two-level system -- a qubit -- is used as a probe of a larger system, it naturally leads to answering a single yes-no question about the system state. Here we propose a method where a single qubit is able to extract, not a single, but many bits of information about the photon number of a microwave resonator using continuous measurement. We realize a proof-of-principle experiment by recordin…
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When a two-level system -- a qubit -- is used as a probe of a larger system, it naturally leads to answering a single yes-no question about the system state. Here we propose a method where a single qubit is able to extract, not a single, but many bits of information about the photon number of a microwave resonator using continuous measurement. We realize a proof-of-principle experiment by recording the fluorescence emitted by a superconducting qubit reflecting a frequency comb, thus implementing multiplexed photon counting where the information about each Fock state -- from 0 to 8 -- is simultaneously encoded in independent measurement channels. Direct Wigner tomography of the quantum state of the resonator evidences the back-action of the measurement as well as the optimal information extraction parameters. Our experiment unleashes the full potential of quantum meters by replacing a sequential quantum measurements with simultaneous and continuous measurements separated in the frequency domain.
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Submitted 2 July, 2021; v1 submitted 9 January, 2020;
originally announced January 2020.
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Sequential dispersive measurement of a superconducting qubit
Authors:
Théau Peronnin,
Danijela Marković,
Quentin Ficheux,
Benjamin Huard
Abstract:
We present a superconducting device that realizes the sequential measurement of a transmon qubit. The device disables common limitations of dispersive readout such as Purcell effect or transients in the cavity mode by turning on and off the coupling to the measurement channel on demand. The qubit measurement begins by loading a readout resonator that is coupled to the qubit. After an optimal inter…
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We present a superconducting device that realizes the sequential measurement of a transmon qubit. The device disables common limitations of dispersive readout such as Purcell effect or transients in the cavity mode by turning on and off the coupling to the measurement channel on demand. The qubit measurement begins by loading a readout resonator that is coupled to the qubit. After an optimal interaction time with negligible loss, a microwave pump releases the content of the readout mode by upconversion into a measurement line in a characteristic time as low as 10~ns, which is 400 times shorter than the lifetime of the readout resonator. A direct measurement of the released field quadratures demonstrates a readout fidelity of $97.5~\%$ in a total measurement time of $220~\mathrm{ns}$. The Wigner tomography of the readout mode allows us to characterize the non-Gaussian nature of the readout mode and its dynamics.
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Submitted 21 April, 2020; v1 submitted 9 April, 2019;
originally announced April 2019.
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Injection locking and parametric locking in a superconducting circuit
Authors:
Danijela Marković,
Jean-Damien Pillet,
Emmanuel Flurin,
Nicolas Roch,
Benjamin Huard
Abstract:
When a signal is injected in a parametric oscillator close enough to its resonance, the oscillator frequency and phase get locked to those of the injected signal. Here, we demonstrate two frequency locking schemes using a Josephson mixer in the parametric down-conversion regime, pumped beyond the parametric oscillation threshold. The circuit then emits radiation out of two spectraly and spatially…
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When a signal is injected in a parametric oscillator close enough to its resonance, the oscillator frequency and phase get locked to those of the injected signal. Here, we demonstrate two frequency locking schemes using a Josephson mixer in the parametric down-conversion regime, pumped beyond the parametric oscillation threshold. The circuit then emits radiation out of two spectraly and spatially separated resonators at frequencies determined by the locking schemes that we choose. When we inject the signal close to a resonance, it locks the oscillator emission to the signal frequency by injection locking. When we inject the signal close to the difference of resonances, it locks the oscillator emission by parametric locking. We compare both schemes and investigate the dependence of the parametric locking range on the pump and the injection signal power. Our results can be interpreted using Adler's theory for lasers, which makes a new link between laser physics and superconducting circuits that could enable better understanding of pumped circuits for quantum information applications such as error correction, circulators and photon number detectors.
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Submitted 27 July, 2019; v1 submitted 2 April, 2019;
originally announced April 2019.
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Maxwell's demon in superconducting circuits
Authors:
Nathanaël Cottet,
Benjamin Huard
Abstract:
This paper provides an overview of the first experimental realizations of quantum-mechanical Maxwell's demons based on superconducting circuits. The principal results of these experiments are recalled and put into context. We highlight the versatility offered by superconducting circuits for studying quantum thermodynamics.
This paper provides an overview of the first experimental realizations of quantum-mechanical Maxwell's demons based on superconducting circuits. The principal results of these experiments are recalled and put into context. We highlight the versatility offered by superconducting circuits for studying quantum thermodynamics.
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Submitted 11 April, 2019; v1 submitted 3 May, 2018;
originally announced May 2018.
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Demonstration of an effective ultrastrong coupling between two oscillators
Authors:
Danijela Marković,
Sébastien Jezouin,
Quentin Ficheux,
Serguei Fedortchenko,
Simone Felicetti,
Thomas Coudreau,
Perola Milman,
Zaki Leghtas,
Benjamin Huard
Abstract:
When the coupling rate between two quantum systems becomes as large as their characteristic frequencies, it induces dramatic effects on their dynamics and even on the nature of their ground state. The case of a qubit coupled to a harmonic oscillator in this ultrastrong coupling regime has been investigated theoretically and experimentally. Here, we explore the case of two harmonic oscillators in t…
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When the coupling rate between two quantum systems becomes as large as their characteristic frequencies, it induces dramatic effects on their dynamics and even on the nature of their ground state. The case of a qubit coupled to a harmonic oscillator in this ultrastrong coupling regime has been investigated theoretically and experimentally. Here, we explore the case of two harmonic oscillators in the ultrastrong coupling regime. Specifically, we realize an analog quantum simulation of this coupled system by dual frequency pumping a nonlinear superconducting circuit. The pump amplitudes directly tune the effective coupling rate. We observe spectroscopic signature of a mode hybridization that is characteristic of the ultrastrong coupling. Further we experimentally demon- strate a key property of the ground state of this simulated ultrastrong coupling between modes by observing simultaneous single-mode and two-mode squeezing of the radiated field below vacuum fluctuations.
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Submitted 23 April, 2018;
originally announced April 2018.
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Dynamics of a qubit while simultaneously monitoring its relaxation and dephasing
Authors:
Q. Ficheux,
S. Jezouin,
Z. Leghtas,
B. Huard
Abstract:
Decoherence originates from the leakage of quantum information into external degrees of freedom. For a qubit the two main decoherence channels are relaxation and dephasing. Here, we report an experiment on a superconducting qubit where we retrieve part of the lost information in both of these channels. We demonstrate that raw averaging the corresponding measurement records provides a full quantum…
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Decoherence originates from the leakage of quantum information into external degrees of freedom. For a qubit the two main decoherence channels are relaxation and dephasing. Here, we report an experiment on a superconducting qubit where we retrieve part of the lost information in both of these channels. We demonstrate that raw averaging the corresponding measurement records provides a full quantum tomography of the qubit state where all three components of the effective spin-1/2 are simultaneously measured. From single realizations of the experiment, it is possible to infer the quantum trajectories followed by the qubit state conditioned on relaxation and/or dephasing channels. The incompatibility between these quantum measurements of the qubit leads to observable consequences in the statistics of quantum states. The high level of controllability of superconducting circuits enables us to explore many regimes from the Zeno effect to underdamped Rabi oscillations depending on the relative strengths of driving, dephasing and relaxation.
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Submitted 25 April, 2018; v1 submitted 3 November, 2017;
originally announced November 2017.
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Observing a quantum Maxwell demon at work
Authors:
N. Cottet,
S. Jezouin,
L. Bretheau,
P. Campagne-Ibarcq,
Q. Ficheux,
J. Anders,
A. Auffèves,
R. Azouit,
P. Rouchon,
B. Huard
Abstract:
In apparent contradiction to the laws of thermodynamics, Maxwell's demon is able to cyclically extract work from a system in contact with a thermal bath exploiting the information about its microstate. The resolution of this paradox required the insight that an intimate relationship exists between information and thermodynamics. Here, we realize a Maxwell demon experiment that tracks the state of…
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In apparent contradiction to the laws of thermodynamics, Maxwell's demon is able to cyclically extract work from a system in contact with a thermal bath exploiting the information about its microstate. The resolution of this paradox required the insight that an intimate relationship exists between information and thermodynamics. Here, we realize a Maxwell demon experiment that tracks the state of each constituent both in the classical and quantum regimes. The demon is a microwave cavity that encodes quantum information about a superconducting qubit and converts information into work by powering up a propagating microwave pulse by stimulated emission. Thanks to the high level of control of superconducting circuits, we directly measure the extracted work and quantify the entropy remaining in the demon's memory. This experiment provides an enlightening illustration of the interplay of thermodynamics with quantum information.
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Submitted 16 February, 2017;
originally announced February 2017.
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Using Spontaneous Emission of a Qubit as a Resource for Feedback Control
Authors:
P. Campagne-Ibarcq,
S. Jezouin,
N. Cottet,
P. Six,
L. Bretheau,
F. Mallet,
A. Sarlette,
P. Rouchon,
B. Huard
Abstract:
Persistent control of a transmon qubit is performed by a feedback protocol based on continuous heterodyne measurement of its fluorescence. By driving the qubit and cavity with microwave signals whose amplitudes depend linearly on the instantaneous values of the quadratures of the measured fluorescence field, we show that it is possible to stabilize permanently the qubit in any targeted state. Usin…
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Persistent control of a transmon qubit is performed by a feedback protocol based on continuous heterodyne measurement of its fluorescence. By driving the qubit and cavity with microwave signals whose amplitudes depend linearly on the instantaneous values of the quadratures of the measured fluorescence field, we show that it is possible to stabilize permanently the qubit in any targeted state. Using a Josephson mixer as a phase-preserving amplifier, it was possible to reach a total measurement efficiency $η$=35%, leading to a maximum of 59% of excitation and 44% of coherence for the stabilized states. The experiment demonstrates multiple-input multiple-output analog Markovian feedback in the quantum regime.
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Submitted 8 August, 2016; v1 submitted 17 February, 2016;
originally announced February 2016.
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Anatomy of Fluorescence: Quantum trajectory statistics from continuously measuring spontaneous emission
Authors:
Andrew N. Jordan,
Areeya Chantasri,
Pierre Rouchon,
Benjamin Huard
Abstract:
We investigate the continuous quantum measurement of a superconducting qubit undergoing fluorescence. The fluorescence of the qubit is detected via a phase-preserving heterodyne measurement, giving the fluorescence quadrature signals as two continuous qubit readout results. By using the stochastic path integral approach to the measurement physics, we derive most likely paths between boundary condi…
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We investigate the continuous quantum measurement of a superconducting qubit undergoing fluorescence. The fluorescence of the qubit is detected via a phase-preserving heterodyne measurement, giving the fluorescence quadrature signals as two continuous qubit readout results. By using the stochastic path integral approach to the measurement physics, we derive most likely paths between boundary conditions on the state, and compute approximate time correlation functions between all stochastic variables via diagrammatic perturbation theory. We focus on paths that increase in energy during the continuous measurement. Our results are compared to Monte Carlo numerical simulation of the trajectories, and we find close agreement between direct simulation and theory. We generalize this analysis to arbitrary diffusive quantum systems that are continuously monitored.
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Submitted 20 November, 2015;
originally announced November 2015.
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Observing quantum state diffusion by heterodyne detection of fluorescence
Authors:
P. Campagne-Ibarcq,
P. Six,
L. Bretheau,
A. Sarlette,
M. Mirrahimi,
P. Rouchon,
B. Huard
Abstract:
A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures con…
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A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures continuously the amplitude of the fluorescence field instead? Using a superconducting parametric amplifier, we have performed heterodyne detection of the fluorescence of a superconducting qubit. For each realization of the measurement record, we can reconstruct a different quantum trajectory for the qubit. The observed evolution obeys quantum state diffusion, which is characteristic of quantum measurements subject to zero point fluctuations. Independent projective measurements of the qubit at various times provide a quantitative validation of the reconstructed trajectories. By exploring the statistics of quantum trajectories, we demonstrate that the qubit states span a deterministic surface in the Bloch sphere at each time in the evolution. Additionally, we show that when monitoring fluorescence, coherent superpositions are generated during the decay from excited to ground state. Counterintuitively, measuring light emitted during relaxation can give rise to trajectories with increased excitation probability.
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Submitted 4 November, 2015;
originally announced November 2015.
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Quantum dynamics of an electromagnetic mode that cannot contain N photons
Authors:
Landry Bretheau,
Philippe Campagne-Ibarcq,
Emmanuel Flurin,
François Mallet,
Benjamin Huard
Abstract:
Electromagnetic modes are instrumental in building quantum machines. In this experiment, we introduce a method to manipulate these modes by effectively controlling their phase space. Preventing access to a single energy level, corresponding to a number of photons N, confined the dynamics of the field to levels 0 to N-1. Under a resonant drive, the level occupation was found to oscillate in time, s…
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Electromagnetic modes are instrumental in building quantum machines. In this experiment, we introduce a method to manipulate these modes by effectively controlling their phase space. Preventing access to a single energy level, corresponding to a number of photons N, confined the dynamics of the field to levels 0 to N-1. Under a resonant drive, the level occupation was found to oscillate in time, similarly to an N-level system. Performing a direct Wigner tomography of the field revealed its nonclassical features, including a Schrödinger cat-like state at half period in the evolution. This fine control of the field in its phase space may enable applications in quantum information and metrology.
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Submitted 18 May, 2015; v1 submitted 15 May, 2015;
originally announced May 2015.
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A compact design for the Josephson mixer: the lumped element circuit
Authors:
J. -D. Pillet,
E. Flurin,
F. Mallet,
B. Huard
Abstract:
We present a compact and efficient design in terms of gain, bandwidth and dynamical range for the Josephson mixer, the superconducting circuit performing three-wave mixing at microwave frequencies. In an all lumped-element based circuit with galvanically coupled ports, we demonstrate non degenerate amplification for microwave signals over a bandwidth up to 50 MHz for a power gain of 20 dB. The qua…
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We present a compact and efficient design in terms of gain, bandwidth and dynamical range for the Josephson mixer, the superconducting circuit performing three-wave mixing at microwave frequencies. In an all lumped-element based circuit with galvanically coupled ports, we demonstrate non degenerate amplification for microwave signals over a bandwidth up to 50 MHz for a power gain of 20 dB. The quantum efficiency of the mixer is shown to be about 70$\%$ and its saturation power reaches $-112$ dBm.
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Submitted 8 June, 2015; v1 submitted 27 March, 2015;
originally announced March 2015.
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Superconducting quantum node for entanglement and storage of microwave radiation
Authors:
Emmanuel Flurin,
Nicolas Roch,
Jean-Damien Pillet,
François Mallet,
Benjamin Huard
Abstract:
Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage and retrieval of an optimally shaped propagat…
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Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the timed-controlled generation of an entangled state distributed between the node and a microwave channel.
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Submitted 4 February, 2015; v1 submitted 22 January, 2014;
originally announced January 2014.
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Persistent control of a superconducting qubit by stroboscopic measurement feedback
Authors:
Philippe Campagne-Ibarcq,
Emmanuel Flurin,
Nicolas Roch,
David Darson,
Pascal Morfin,
Mazyar Mirrahimi,
Michel H. Devoret,
Francois Mallet,
Benjamin Huard
Abstract:
Making a system state follow a prescribed trajectory despite fluctuations and errors commonly consists in monitoring an observable (temperature, blood-glucose level...) and reacting on its controllers (heater power, insulin amount ...). In the quantum domain, there is a change of paradigm in feedback since measurements modify the state of the system, most dramatically when the trajectory goes thro…
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Making a system state follow a prescribed trajectory despite fluctuations and errors commonly consists in monitoring an observable (temperature, blood-glucose level...) and reacting on its controllers (heater power, insulin amount ...). In the quantum domain, there is a change of paradigm in feedback since measurements modify the state of the system, most dramatically when the trajectory goes through superpositions of measurement eigenstates. Here, we demonstrate the stabilization of an arbitrary trajectory of a superconducting qubit by measurement based feedback. The protocol benefits from the long coherence time ($T_2>10 μ$s) of the 3D transmon qubit, the high efficiency (82%) of the phase preserving Josephson amplifier, and fast electronics ensuring less than 500 ns delay. At discrete time intervals, the state of the qubit is measured and corrected in case an error is detected. For Rabi oscillations, where the discrete measurements occur when the qubit is supposed to be in the measurement pointer states, we demonstrate an average fidelity of 85% to the targeted trajectory. For Ramsey oscillations, which does not go through pointer states, the average fidelity reaches 75%. Incidentally, we demonstrate a fast reset protocol allowing to cool a 3D transmon qubit down to 0.6% in the excited state.
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Submitted 21 August, 2013; v1 submitted 25 January, 2013;
originally announced January 2013.
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Generating Entangled Microwave Radiation Over Two Transmission Lines
Authors:
Emmanuel Flurin,
Nicolas Roch,
Francois Mallet,
Michel H. Devoret,
Benjamin Huard
Abstract:
Using a superconducting circuit, the Josephson mixer, we demonstrate the first experimental realization of spatially separated two-mode squeezed states of microwave light. Driven by a pump tone, a first Josephson mixer generates, out of quantum vacuum, a pair of entangled fields at different frequencies on separate transmission lines. A second mixer, driven by a $π$-phase shifted copy of the first…
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Using a superconducting circuit, the Josephson mixer, we demonstrate the first experimental realization of spatially separated two-mode squeezed states of microwave light. Driven by a pump tone, a first Josephson mixer generates, out of quantum vacuum, a pair of entangled fields at different frequencies on separate transmission lines. A second mixer, driven by a $π$-phase shifted copy of the first pump tone, recombines and disentangles the two fields. The resulting output noise level is measured to be lower than for vacuum state at the input of the second mixer, an unambiguous proof of entanglement. Moreover, the output noise level provides a direct, quantitative measure of entanglement, leading here to the demonstration of 6 Mebit.s$^{-1}$ (Mega entangled bits per second) generated by the first mixer.
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Submitted 31 October, 2012; v1 submitted 3 April, 2012;
originally announced April 2012.
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Widely tunable, non-degenerate three-wave mixing microwave device operating near the quantum limit
Authors:
Nicolas Roch,
Emmanuel Flurin,
François Nguyen,
Pascal Morfin,
Philippe Campagne-Ibarcq,
Michel H. Devoret,
Benjamin Huard
Abstract:
We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions shunted by a cross of four linear inductances. The phase configuration of the ring remains unique over a wide range of magnetic fluxes threading…
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We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions shunted by a cross of four linear inductances. The phase configuration of the ring remains unique over a wide range of magnetic fluxes threading the loop. It is thus possible to vary the inductance of the ring with flux while retaining a strong, dissipation-free, and noiseless non-linearity. The device has been operated in amplifier mode and its noise performance has been evaluated by using the noise spectrum emitted by a voltage biased tunnel junction at finite frequency as a test signal. The unprecedented accuracy with which the crossover between zero-point-fluctuations and shot noise has been measured provides an upper-bound for the noise and dissipation intrinsic to the device.
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Submitted 6 February, 2012;
originally announced February 2012.
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Coupling a quantum dot, fermionic leads and a microwave cavity on-chip
Authors:
M. R. Delbecq,
V. Schmitt,
F. D. Parmentier,
N. Roch,
J. J. Viennot,
G. Fève,
B. Huard,
C. Mora,
A. Cottet,
T. Kontos
Abstract:
We demonstrate a hybrid architecture consisting of a quantum dot circuit coupled to a single mode of the electromagnetic field. We use single wall carbon nanotube based circuits inserted in superconducting microwave cavities. By probing the nanotube-dot using a dispersive read-out in the Coulomb blockade and the Kondo regime, we determine an electron-photon coupling strength which should enable ci…
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We demonstrate a hybrid architecture consisting of a quantum dot circuit coupled to a single mode of the electromagnetic field. We use single wall carbon nanotube based circuits inserted in superconducting microwave cavities. By probing the nanotube-dot using a dispersive read-out in the Coulomb blockade and the Kondo regime, we determine an electron-photon coupling strength which should enable circuit QED experiments with more complex quantum dot circuits.
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Submitted 22 August, 2011;
originally announced August 2011.
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Transport scattering time probed through rf admittance of a graphene capacitor
Authors:
E. Pallecchi,
A. C. Betz,
J. Chaste,
G. Fève,
B. Huard,
T. Kontos,
J. -M. Berroir,
B. Plaçais
Abstract:
We have investigated electron dynamics in top gated graphene by measuring the gate admittance of a diffusive graphene capacitor in a broad frequency range as a function of carrier density. The density of states, conductivity and diffusion constant are deduced from the low frequency gate capacitance, its charging time and their ratio. The admittance evolves from an RC-like to a skin-effect response…
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We have investigated electron dynamics in top gated graphene by measuring the gate admittance of a diffusive graphene capacitor in a broad frequency range as a function of carrier density. The density of states, conductivity and diffusion constant are deduced from the low frequency gate capacitance, its charging time and their ratio. The admittance evolves from an RC-like to a skin-effect response at GHz frequency with a crossover given by the Thouless energy. The scattering time is found to be independent of energy in the 0 - 200 meV investigated range at room temperature. This is consistent with a random mass model for Dirac Fermions.
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Submitted 23 March, 2011; v1 submitted 19 May, 2010;
originally announced May 2010.
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Contact resistance and shot noise in graphene transistors
Authors:
J. Cayssol,
B. Huard,
D. Goldhaber-Gordon
Abstract:
Potential steps naturally develop in graphene near metallic contacts. We investigate the influence of these steps on the transport in graphene Field Effect Transistors. We give simple expressions to estimate the voltage-dependent contribution of the contacts to the total resistance and noise in the diffusive and ballistic regimes.
Potential steps naturally develop in graphene near metallic contacts. We investigate the influence of these steps on the transport in graphene Field Effect Transistors. We give simple expressions to estimate the voltage-dependent contribution of the contacts to the total resistance and noise in the diffusive and ballistic regimes.
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Submitted 20 December, 2008; v1 submitted 24 October, 2008;
originally announced October 2008.
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Evidence of Klein tunneling in graphene p-n junctions
Authors:
N. Stander,
B. Huard,
D. Goldhaber-Gordon
Abstract:
Transport through potential barriers in graphene is investigated using a set of metallic gates capacitively coupled to graphene to modulate the potential landscape. When a gate-induced potential step is steep enough, disorder becomes less important and the resistance across the step is in quantitative agreement with predictions of Klein tunneling of Dirac fermions up to a small correction. We al…
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Transport through potential barriers in graphene is investigated using a set of metallic gates capacitively coupled to graphene to modulate the potential landscape. When a gate-induced potential step is steep enough, disorder becomes less important and the resistance across the step is in quantitative agreement with predictions of Klein tunneling of Dirac fermions up to a small correction. We also perform magnetoresistance measurements at low magnetic fields and compare them to recent predictions.
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Submitted 30 November, 2008; v1 submitted 13 June, 2008;
originally announced June 2008.
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Evidence of the role of contacts on the observed electron-hole asymmetry in graphene
Authors:
B. Huard,
N. Stander,
J. A. Sulpizio,
D. Goldhaber-Gordon
Abstract:
We perform electrical transport measurements in graphene with several sample geometries. In particular, we design ``invasive'' probes crossing the whole graphene sheet as well as ``external'' probes connected through graphene side arms. The four-probe conductance measured between external probes varies linearly with charge density and is symmetric between electron and hole types of carriers. In…
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We perform electrical transport measurements in graphene with several sample geometries. In particular, we design ``invasive'' probes crossing the whole graphene sheet as well as ``external'' probes connected through graphene side arms. The four-probe conductance measured between external probes varies linearly with charge density and is symmetric between electron and hole types of carriers. In contrast measurements with invasive probes give a strong electron-hole asymmetry and a sub-linear conductance as a function of density. By comparing various geometries and types of contact metal, we show that these two observations are due to transport properties of the metal/graphene interface. The asymmetry originates from the pinning of the charge density below the metal, which thereby forms a p-n or p-p junction depending on the polarity of the carriers in the bulk graphene sheet. Our results also explain part of the sub-linearity observed in conductance as a function of density in a large number of experiments on graphene, which has generally been attributed to short-range scattering only.
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Submitted 12 April, 2008;
originally announced April 2008.
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Josephson junctions as detectors for non-Gaussian noise
Authors:
B. Huard,
H. Pothier,
Norman O. Birge,
D. Esteve,
X. Waintal,
J. Ankerhold
Abstract:
Non-Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on-chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased…
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Non-Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on-chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased effective temperature, but also the noise asymmetry. A theoretical description of the thermal escape of a Josephson junction in presence of noise with a non-zero third cumulant is presented, together with numerical simulations when the noise source is a tunnel junction with Poisson noise. Comparison between experiment and theory is discussed.
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Submitted 5 November, 2007;
originally announced November 2007.
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Electron heating in metallic resistors at sub-Kelvin temperature
Authors:
B. Huard,
H. Pothier,
D. Esteve,
K. E. Nagaev
Abstract:
In the presence of Joule heating, the electronic temperature in a metallic resistor placed at sub-Kelvin temperatures can significantly exceed the phonon temperature. Electron cooling proceeds mainly through two processes: electronic diffusion to and from the connecting wires and electron-phonon coupling. The goal of this paper is to present a general solution of the problem, in a form that can…
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In the presence of Joule heating, the electronic temperature in a metallic resistor placed at sub-Kelvin temperatures can significantly exceed the phonon temperature. Electron cooling proceeds mainly through two processes: electronic diffusion to and from the connecting wires and electron-phonon coupling. The goal of this paper is to present a general solution of the problem, in a form that can easily be used in practical situations. As an application, we compute two quantities that depend on the electronic temperature profile: the second and the third cumulant of the current noise at zero frequency, as a function of the voltage across the resistor. We also consider time dependent heating, an issue relevant for experiments in which current pulses are used, for instance in time-resolved calorimetry experiments.
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Submitted 6 September, 2007; v1 submitted 29 August, 2007;
originally announced August 2007.
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Measurement of the current-phase relation of superconducting atomic contacts
Authors:
M. L. Della Rocca,
M. Chauvin,
B. Huard,
H. Pothier,
D. Esteve,
C. Urbina
Abstract:
We have probed the current-phase relation of an atomic contact placed with a tunnel junction in a small superconducting loop. The measurements are in quantitative agreement with the predictions of a resistively shunted SQUID model in which the Josephson coupling of the contact is calculated using the independently determined transmissions of its conduction channels.
We have probed the current-phase relation of an atomic contact placed with a tunnel junction in a small superconducting loop. The measurements are in quantitative agreement with the predictions of a resistively shunted SQUID model in which the Josephson coupling of the contact is calculated using the independently determined transmissions of its conduction channels.
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Submitted 6 August, 2007; v1 submitted 3 August, 2007;
originally announced August 2007.
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Transport measurements across a tunable potential barrier in graphene
Authors:
B. Huard,
J. A. Sulpizio,
N. Stander,
K. Todd,
B. Yang,
D. Goldhaber-Gordon
Abstract:
The peculiar nature of electron scattering in graphene is among many exciting theoretical predictions for the physical properties of this material. To investigate electron scattering properties in a graphene plane, we have created a gate-tunable potential barrier within a single-layer graphene sheet. We report measurements of electrical transport across this structure as the tunable barrier pote…
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The peculiar nature of electron scattering in graphene is among many exciting theoretical predictions for the physical properties of this material. To investigate electron scattering properties in a graphene plane, we have created a gate-tunable potential barrier within a single-layer graphene sheet. We report measurements of electrical transport across this structure as the tunable barrier potential is swept through a range of heights. When the barrier is sufficiently strong to form a bipolar junctions (npn or pnp) within the graphene sheet, the resistance across the barrier sharply increases. We compare these results to predictions for both diffusive and ballistic transport, as the barrier rises on a length scale comparable to the mean free path. Finally, we show how a magnetic field modifies transport across the barrier.
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Submitted 7 June, 2007; v1 submitted 19 April, 2007;
originally announced April 2007.
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Effect of Magnetic Impurities on Energy Exchange between Electrons
Authors:
B. Huard,
A. Anthore,
Norman O. Birge,
H. Pothier,
D. Esteve
Abstract:
In order to probe quantitatively the effect of Kondo impurities on energy exchange between electrons in metals, we have compared measurements on two silver wires with dilute magnetic impurities (manganese) introduced in one of them. The measurement of the temperature dependence of the electron phase coherence time on the wires provides an independent determination of the impurity concentration.…
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In order to probe quantitatively the effect of Kondo impurities on energy exchange between electrons in metals, we have compared measurements on two silver wires with dilute magnetic impurities (manganese) introduced in one of them. The measurement of the temperature dependence of the electron phase coherence time on the wires provides an independent determination of the impurity concentration. Quantitative agreement on the energy exchange rate is found with a theory by Göppert et al. that accounts for Kondo scattering of electrons on spin-1/2 impurities.
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Submitted 26 July, 2005;
originally announced July 2005.
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Intensity of Coulomb Interaction between quasiparticles in diffusive metallic wires
Authors:
B. Huard,
A. Anthore,
F. Pierre,
H. Pothier,
Norman O. Birge,
D. Esteve
Abstract:
The energy dependence and intensity of Coulomb interaction between quasiparticles in metallic wires is obtained from two different methods: determination of the temperature dependence of the phase coherence time from the magnetoresistance, and measurements of the energy distribution function in out-of-equilibrium situations. In both types of experiment, the energy dependence of the Coulomb inter…
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The energy dependence and intensity of Coulomb interaction between quasiparticles in metallic wires is obtained from two different methods: determination of the temperature dependence of the phase coherence time from the magnetoresistance, and measurements of the energy distribution function in out-of-equilibrium situations. In both types of experiment, the energy dependence of the Coulomb interaction is found to be in excellent agreement with theoretical predictions. In contrast, the intensity of the interaction agrees closely with theory only with the first method, whereas an important discrepancy is found using the second one. Different explanations are proposed, and results of a test experiment are presented.
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Submitted 8 April, 2004;
originally announced April 2004.