Showing 1–23 of 23 results for author: Franz, T

Emergence of spin entanglement with the pseudogap onset in the Fermi-Hubbard model

Authors: Frederic Bippus, Thomas Chalopin, Gabriele Bellomia, Gergő Roósz, Titus Franz, Antoine Georges, Anna Kauch, Immanuel Bloch, Karsten Held

Abstract: Despite decades of intense theoretical and experimental investigation, the two-dimensional Fermi-Hubbard model still resists a complete microscopic understanding. Conventional approaches typically probe global observables and locally resolved correlation functions. Here, we develop a complementary perspective based on the measurement of entanglement. Using both an ultracold-atom quantum simulator… ▽ More Despite decades of intense theoretical and experimental investigation, the two-dimensional Fermi-Hubbard model still resists a complete microscopic understanding. Conventional approaches typically probe global observables and locally resolved correlation functions. Here, we develop a complementary perspective based on the measurement of entanglement. Using both an ultracold-atom quantum simulator and numerical simulations based on the dynamical vertex approximation, we find that entanglement is closely tied to the onset of the enigmatic pseudogap regime: spin-singlet entanglement emerges only as the pseudogap sets in and, in contrast to classical correlations, remains confined to nearest-neighbour sites in this regime. Our results, therefore, disfavour purely classical-fluctuation theories of the pseudogap and constrain microscopic models to those that develop nearest-neighbour spin-singlet entanglement at the pseudogap onset. △ Less

Submitted 29 May, 2026; originally announced May 2026.

Comments: 8 figures, 34 pages

Observation of Strong-to-Weak Spontaneous Symmetry Breaking in a Dephased Fermi Gas

Authors: Si Wang, Thomas G. Kiely, Dorothee Tell, Johannes Obermeyer, Marnix Barendregt, Petar Bojović, Philipp M. Preiss, Abhijat Sarma, Titus Franz, Matthew P. A. Fisher, Cenke Xu, Immanuel Bloch

Abstract: Symmetry-based classification of quantum phases of matter is one of the most foundational organizing principles in physics; however, an analogous framework for mixed, decohered quantum states has only begun to emerge. A central new concept is strong-to-weak spontaneous symmetry breaking (SW-SSB), a sharp transition in mixed quantum states that is invisible to any observable linear in the density m… ▽ More Symmetry-based classification of quantum phases of matter is one of the most foundational organizing principles in physics; however, an analogous framework for mixed, decohered quantum states has only begun to emerge. A central new concept is strong-to-weak spontaneous symmetry breaking (SW-SSB), a sharp transition in mixed quantum states that is invisible to any observable linear in the density matrix and that has since been predicted across a broad class of open and monitored quantum systems. It also provides a unifying language for phenomena as disparate as the decodability of topological quantum memories and the emergence of classical hydrodynamics from decohered quantum dynamics. Here we report the first experimental observation of SW-SSB, in dephased single-component fermionic matter imaged by a quantum gas microscope. A quantum-classical estimator built on a machine-learned Gaussian reference state gives direct access to the nonlinear Rényi-1 and Rényi-2 correlators that diagnose SW-SSB, and reveals long-range Rényi order in the dephased Fermi liquid. Adding a commensurate superlattice drives the underlying fermions through a metal-to-insulator transition that, after full dephasing, manifests as a sharp SW-SSB phase transition. Our results uncover the symmetry principle behind information-theoretic transitions in open quantum systems, and extend Landau's symmetry paradigm into the regime of real, decohering quantum devices. △ Less

Submitted 17 April, 2026; originally announced April 2026.

Realizing the Emery Model in Optical Lattices for Quantum Simulation of Cuprates and Nickelates

Authors: Hannah Lange, Liyang Qiu, Robin Groth, Andreas von Haaren, Luca Muscarella, Titus Franz, Immanuel Bloch, Fabian Grusdt, Philipp M. Preiss, Annabelle Bohrdt

Abstract: The microscopic origin of high-temperature superconductivity in cuprates remains one of the central open questions in condensed matter physics. Growing experimental and theoretical evidence suggests that the bare single-band Fermi-Hubbard model may not fully capture properties of cuprates such as superconductivity, motivating us to revisit the canonical three-band model of the copper-oxide planes… ▽ More The microscopic origin of high-temperature superconductivity in cuprates remains one of the central open questions in condensed matter physics. Growing experimental and theoretical evidence suggests that the bare single-band Fermi-Hubbard model may not fully capture properties of cuprates such as superconductivity, motivating us to revisit the canonical three-band model of the copper-oxide planes - the Emery model - from which the single-band counterpart was originally derived. Here, we propose and analyze a quantum simulation scheme for realizing the Emery model in regimes relevant to cuprates and infinite-layer nickelates with today's ultracold atom quantum simulation platforms, enabling the exploration of the three-band physics on system sizes that are challenging for current numerical methods. Specifically, we show that a two-dimensional optical lattice with a superimposed pattern of repulsive potentials can be designed to study low-temperature properties for variable parameter regimes of the Emery model relevant to cuprates as well as infinite-layer nickelates. Our results pave the way for real material simulations with ultracold atom quantum simulators and a better understanding of the physics of unconventional superconductors. △ Less

Submitted 11 March, 2026; originally announced March 2026.

Constructing Arbitrary Coherent Rearrangements in Optical Lattices

Authors: Alexander Roth, Liyang Qiu, Timon Hilker, Titus Franz, Philipp M. Preiss

Abstract: Coherent control of motional degrees of freedom of ultracold atoms in optical lattices offers a promising route towards programmable quantum dynamics with massive particles. We propose and analyze a scheme for implementing coherent rearrangement of ultracold atoms, corresponding to arbitrary unitary transformations on single-particle motional states. Exploiting an analogy between dynamics in optic… ▽ More Coherent control of motional degrees of freedom of ultracold atoms in optical lattices offers a promising route towards programmable quantum dynamics with massive particles. We propose and analyze a scheme for implementing coherent rearrangement of ultracold atoms, corresponding to arbitrary unitary transformations on single-particle motional states. Exploiting an analogy between dynamics in optical superlattices and discrete linear optics, we employ the Clements scheme to systematically construct any global $N$-dimensional single-particle unitary from tunneling and phase shifts in arrays of double wells. Tunneling is controlled globally, while local operations are achieved through site-resolved potential shifts. We numerically investigate the susceptibility of the scheme to intensity noise and addressing crosstalk. We identify key subroutines enabled by this unitary construction, including the Discrete Fourier Transform and the implementation of non-native Hamiltonians. Extending the scheme to two dimensions enables all-to-all atomic rearrangement with a circuit depth that scales sublinearly with the atom number, providing a high-density and highly scalable approach to atom rearrangement. △ Less

Submitted 4 March, 2026; originally announced March 2026.

Comments: 12 pages, 7 figures

Quantum information scrambling in strongly disordered Rydberg spin systems

Authors: Maximilian Müllenbach, Sebastian Geier, Adrian Braemer, Eduard J. Braun, Titus Franz, Gerhard Zürn, Matthias Weidemüller, Martin Gärttner

Abstract: Despite the fact that power-law interactions occur in a plethora of physical systems, their many-body dynamics is far less understood than that of nearest-neighbor interacting systems. Here, we study information scrambling in strongly disordered spin systems with power-law interactions via out-of-time-order correlators (OTOCs). Numerically, we find pronounced differences in the dynamical spreading… ▽ More Despite the fact that power-law interactions occur in a plethora of physical systems, their many-body dynamics is far less understood than that of nearest-neighbor interacting systems. Here, we study information scrambling in strongly disordered spin systems with power-law interactions via out-of-time-order correlators (OTOCs). Numerically, we find pronounced differences in the dynamical spreading of OTOCs between nearest-neighbor and power-law interacting systems. This deviation persists even for short-range interactions, opposing the common view that these interactions produce dynamics equivalent to the nearest-neighbor case. In a detailed experimental proposal, tailored but not limited to Rydberg tweezer setups, we present a protocol to extract OTOCs in XXZ Heisenberg spin systems with tunable anisotropy and programmable disorder based on currently available techniques. △ Less

Submitted 26 July, 2026; v1 submitted 22 December, 2025; originally announced December 2025.

Comments: 8 pages, 5 figures

Phase-Sensitive Measurements on a Fermi-Hubbard Quantum Processor

Authors: Alberto R. Cavallar, Luis Escalera-Moreno, Titus Franz, Timon Hilker, J. Ignacio Cirac, Philipp M. Preiss, Benjamin F. Schiffer

Abstract: Fermionic quantum processors are a promising platform for quantum simulation of correlated fermionic matter. In this work, we study a hardware-efficient protocol for measuring complex expectation values of the time-evolution operator, commonly referred to as Loschmidt echoes, with fermions in an optical superlattice. We analyze the algorithm for the Fermi-Hubbard model at half-filling as well as a… ▽ More Fermionic quantum processors are a promising platform for quantum simulation of correlated fermionic matter. In this work, we study a hardware-efficient protocol for measuring complex expectation values of the time-evolution operator, commonly referred to as Loschmidt echoes, with fermions in an optical superlattice. We analyze the algorithm for the Fermi-Hubbard model at half-filling as well as at finite doping. The method relies on global quench dynamics and short imaginary time evolution, the latter being realized by architecture-tailored pulse sequences starting from a product state of plaquettes. Our numerical results show that complex Loschmidt echoes can be efficiently obtained for large many-body states over a broad spectral range. This allows one to measure spectral properties of the Fermi-Hubbard model, such as the local density of states, and paves the way for the study of finite-temperature properties in current fermionic quantum simulators. △ Less

Submitted 4 May, 2026; v1 submitted 1 September, 2025; originally announced September 2025.

Comments: 10+7 pages, 5+6 figures, final version accepted for publication in Quantum

Journal ref: Quantum 10, 2103 (2026)

Observation of hysteresis in an isolated quantum system of disordered Heisenberg spins

Authors: Moritz Hornung, Eduard J. Braun, Sebastian Geier, Titus Franz, Gerhard Zürn, Matthias Weidemüller

Abstract: We find energy-dependent hysteresis in an isolated Heisenberg quantum spin system, similar to thermomagnetic hysteresis in canonical spin glasses in contact with a thermal reservoir. Analogous to zero-field cooling and field cooling in conventional magnetic materials, an annealing protocol is devised to control the energy in an isolated system. Depending on the strength of disorder, the susceptibi… ▽ More We find energy-dependent hysteresis in an isolated Heisenberg quantum spin system, similar to thermomagnetic hysteresis in canonical spin glasses in contact with a thermal reservoir. Analogous to zero-field cooling and field cooling in conventional magnetic materials, an annealing protocol is devised to control the energy in an isolated system. Depending on the strength of disorder, the susceptibilities at zero field bifurcate at a specific energy, which signals the presence of different magnetic regimes. This behavior is apparent both in a numerical simulation by exact diagonalization of the Heisenberg Hamiltonian with twelve particles, as well as in an experiment with thousands of Rydberg atoms representing dipolar interacting quantum spins. The annealing protocols open a new path to explore the energy-dependent phase structure of spin systems at low energies. Our observation of a nonthermal metastable regime might indicate the existence of a phase transition to a novel state of isolated quantum spin systems. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 6 pages, 2 figures, 1 supplement

High-fidelity collisional quantum gates with fermionic atoms

Authors: Petar Bojović, Timon Hilker, Si Wang, Johannes Obermeyer, Marnix Barendregt, Dorothee Tell, Thomas Chalopin, Philipp M. Preiss, Immanuel Bloch, Titus Franz

Abstract: Quantum simulations of electronic structure and strongly correlated quantum phases are widely regarded as among the most promising applications of quantum computing. These computations naturally benefit from native fermionic encodings, which intrinsically restrict the Hilbert space to physical states consistent with fermionic statistics and conservation laws like particle number and magnetization… ▽ More Quantum simulations of electronic structure and strongly correlated quantum phases are widely regarded as among the most promising applications of quantum computing. These computations naturally benefit from native fermionic encodings, which intrinsically restrict the Hilbert space to physical states consistent with fermionic statistics and conservation laws like particle number and magnetization independent of gate errors. While ultracold atoms in optical lattices are established as powerful analog simulators of strongly correlated fermionic matter, neutral-atom platforms have concurrently emerged as versatile, scalable architectures for spin-based digital quantum computation. Unifying these capabilities requires high-fidelity gates that preserve motional degrees of freedom of fermionic atoms, paving the way for a new generation of programmable fermionic quantum processors. Here we demonstrate collisional entangling gates with fidelities up to 99.75(6)% and Bell state lifetimes exceeding $10\,s$, realized via controlled interactions of fermionic atoms in an optical superlattice. Using quantum gas microscopy, we microscopically characterize spin-exchange and pair-tunneling gates, and realize a robust, composite pair-exchange gate, a fundamental primitive for quantum chemistry simulations. Our results establish controlled collisions in optical lattices as a competitive and complementary approach to high entangling gate fidelities in neutral-atom quantum computers. When embedded within a fermionic architecture, this capability enables the preparation of complex quantum states and advanced readout protocols for a new class of scalable analog-digital hybrid quantum simulators. Combined with local addressing, these gates mark a crucial step towards a fully digital fermionic quantum computer based on the controlled motion and entanglement of fermionic neutral atoms. △ Less

Submitted 24 April, 2026; v1 submitted 17 June, 2025; originally announced June 2025.

Comments: 16 pages, 18 figures, accepted version

Journal ref: Nature 652, 602-608 (2026)

Observation of emergent scaling of spin-charge correlations at the onset of the pseudogap

Authors: Thomas Chalopin, Petar Bojović, Si Wang, Titus Franz, Aritra Sinha, Zhenjiu Wang, Dominik Bourgund, Johannes Obermeyer, Fabian Grusdt, Annabelle Bohrdt, Lode Pollet, Alexander Wietek, Antoine Georges, Timon Hilker, Immanuel Bloch

Abstract: In strongly correlated materials, interacting electrons are entangled and form collective quantum states, resulting in rich low-temperature phase diagrams. Notable examples include cuprate superconductors, in which superconductivity emerges at low doping out of an unusual "pseudogap" metallic state above the critical temperature. The Fermi-Hubbard model, describing a wide range of phenomena associ… ▽ More In strongly correlated materials, interacting electrons are entangled and form collective quantum states, resulting in rich low-temperature phase diagrams. Notable examples include cuprate superconductors, in which superconductivity emerges at low doping out of an unusual "pseudogap" metallic state above the critical temperature. The Fermi-Hubbard model, describing a wide range of phenomena associated with strong electron correlations, still offers major computational challenges despite its simple formulation. In this context, ultracold atoms quantum simulators have provided invaluable insights into the microscopic nature of correlated quantum states. Here, we use a quantum gas microscope Fermi-Hubbard simulator to explore a wide range of dopings and temperatures in a regime where a pseudogap is known to develop. By measuring multi-point correlation functions up to fifth order, we uncover a novel universal scaling behaviour in magnetic and higher-order spin-charge correlations characterised by a doping-dependent temperature scale. Accurate comparisons with determinant Quantum Monte Carlo and Minimally Entangled Typical Thermal States simulations confirm that this temperature scale is comparable to the pseudogap temperature T*. Our quantitative findings reveal a novel qualitative behaviour of magnetic properties and spin-charge correlations in an emergent pseudogap and pave the way towards the exploration of charge pairing and collective phenomena expected at lower temperatures. △ Less

Submitted 27 January, 2026; v1 submitted 23 December, 2024; originally announced December 2024.

Comments: 8 + 11 pages, 5 + 10 figures. Accepted version

Local control and mixed dimensions: Exploring high-temperature superconductivity in optical lattices

Authors: Henning Schlömer, Hannah Lange, Titus Franz, Thomas Chalopin, Petar Bojović, Si Wang, Immanuel Bloch, Timon A. Hilker, Fabian Grusdt, Annabelle Bohrdt

Abstract: The simulation of high-temperature superconducting materials by implementing strongly correlated fermionic models in optical lattices is one of the major objectives in the field of analog quantum simulation. Here we show that local control and optical bilayer capabilities combined with spatially resolved measurements create a versatile toolbox to study fundamental properties of both nickelate and… ▽ More The simulation of high-temperature superconducting materials by implementing strongly correlated fermionic models in optical lattices is one of the major objectives in the field of analog quantum simulation. Here we show that local control and optical bilayer capabilities combined with spatially resolved measurements create a versatile toolbox to study fundamental properties of both nickelate and cuprate high-temperature superconductors. On the one hand, we present a scheme to implement a mixed-dimensional (mixD) bilayer model that has been proposed to capture the essential pairing physics of pressurized bilayer nickelates. This allows for the long-sought realization of a state with long-range superconducting order in current lattice quantum simulation machines. In particular, we show how coherent pairing correlations can be accessed in a partially particle-hole transformed and rotated basis. On the other hand, we demonstrate that control of local gates enables the observation of $d$-wave pairing order in the two-dimensional (single-layer) repulsive Fermi-Hubbard model through the simulation of a system with attractive interactions. Lastly, we introduce a scheme to measure momentum-resolved dopant densities, providing access to observables complementary to solid-state experiments -- which is of particular interest for future studies of the enigmatic pseudogap phase appearing in cuprates. △ Less

Submitted 1 October, 2024; v1 submitted 4 June, 2024; originally announced June 2024.

Comments: 15+5 pages

Optical superlattice for engineering Hubbard couplings in quantum simulation

Authors: Thomas Chalopin, Petar Bojović, Dominik Bourgund, Si Wang, Titus Franz, Immanuel Bloch, Timon Hilker

Abstract: Quantum simulations of Hubbard models with ultracold atoms rely on the exceptional control of coherent motion provided by optical lattices. Here we demonstrate enhanced tunability using an optical superlattice in a fermionic quantum gas microscope. With our phase-stable bichromatic design, we achieve a precise control of tunneling and tilt throughout the lattice, as evidenced by long-lived coheren… ▽ More Quantum simulations of Hubbard models with ultracold atoms rely on the exceptional control of coherent motion provided by optical lattices. Here we demonstrate enhanced tunability using an optical superlattice in a fermionic quantum gas microscope. With our phase-stable bichromatic design, we achieve a precise control of tunneling and tilt throughout the lattice, as evidenced by long-lived coherent double-well oscillations and next-nearest-neighbor quantum walks in a staggered configuration. We furthermore present correlated quantum walks of two particles initiated through a resonant pair-breaking mechanism. Finally, we engineer tunable spin couplings through local offsets and create a spin ladder with ferromagnetic and antiferromagnetic couplings along the rungs and legs, respectively. Our work underscores the high potential of optical superlattices for engineering, simulating, and detecting strongly correlated many-body quantum states. △ Less

Submitted 29 May, 2024; originally announced May 2024.

Formation of stripes in a mixed-dimensional cold-atom Fermi-Hubbard system

Authors: Dominik Bourgund, Thomas Chalopin, Petar Bojović, Henning Schlömer, Si Wang, Titus Franz, Sarah Hirthe, Annabelle Bohrdt, Fabian Grusdt, Immanuel Bloch, Timon A. Hilker

Abstract: The relation between d-wave superconductivity and stripes is fundamental to the understanding of ordered phases in cuprates. While experimentally both phases are found in close proximity, numerical studies on the related Fermi-Hubbard model have long been investigating whether stripes precede, compete or coexist with superconductivity. Such stripes are characterised by interleaved charge and spin… ▽ More The relation between d-wave superconductivity and stripes is fundamental to the understanding of ordered phases in cuprates. While experimentally both phases are found in close proximity, numerical studies on the related Fermi-Hubbard model have long been investigating whether stripes precede, compete or coexist with superconductivity. Such stripes are characterised by interleaved charge and spin density wave ordering where fluctuating lines of dopants separate domains of opposite antiferromagnetic order. Here we show first signatures of stripes in a cold-atom Fermi-Hubbard quantum simulator. By engineering a mixed-dimensional system, we increase their typical energy scales to the spin exchange energy, enabling us to access the interesting crossover temperature regime where stripes begin to form. We observe extended, attractive correlations between hole dopants and find an increased probability to form larger structures akin to stripes. In the spin sector, we study correlation functions up to third order and find results consistent with stripe formation. These higher-order correlation measurements pave the way towards an improved microscopic understanding of the emergent properties of stripes and their relation to other competing phases. More generally, our approach has direct relevance for newly discovered high-temperature superconducting materials in which mixed dimensions play an essential role. △ Less

Submitted 21 December, 2023; originally announced December 2023.

Comments: 16 pages, 21 figures

Journal ref: Nature 637 57-62 (2025)

Angle-resolved photoelectron spectroscopy in a low energy electron microscope

Authors: Alexander Neuhaus, Pascal Dreher, Florian Schütz, Helder Marchetto, Torsten Franz, Frank-J. Meyer zu Heringdorf

Abstract: Spectroscopic photoemission microscopy is a well-established method to investigate the electronic structure of surfaces. In modern photoemission microscopes the electron optics allows imaging of the image plane, momentum plane, or dispersive plane, depending on the lens setting. Furthermore, apertures allow filtering of energy-, real-, and momentum space. Here, we describe how a standard spectrosc… ▽ More Spectroscopic photoemission microscopy is a well-established method to investigate the electronic structure of surfaces. In modern photoemission microscopes the electron optics allows imaging of the image plane, momentum plane, or dispersive plane, depending on the lens setting. Furthermore, apertures allow filtering of energy-, real-, and momentum space. Here, we describe how a standard spectroscopic and low energy electron microscope can be equipped with an additional slit at the entrance of the already present hemispherical analyzer to enable an angle- and energy resolved photoemission mode with micrometer spatial selectivity. We apply a photogrammetric calibration to correct for image distortions of the projective system behind the analyzer and present spectra recorded on Au(111) as a benchmark. Our approach makes data acquisition in energy-momentum space more efficient, which is a necessity for laser-based pump-probe photoemission microscopy with femtosecond time resolution. △ Less

Submitted 17 October, 2023; originally announced October 2023.

Comments: This manuscript has been peer-reviewed and is currently undergoing revision

Journal ref: Struct. Dyn. 10, 064304 (2023)

Pair localization in dipolar systems with tunable positional disorder

Authors: Adrian Braemer, Titus Franz, Matthias Weidemüller, Martin Gärttner

Abstract: Strongly interacting quantum systems subject to quenched disorder exhibit intriguing phenomena such as glassiness and many-body localization. Theoretical studies have mainly focused on disorder in the form of random potentials, while many experimental realizations naturally feature disorder in the interparticle interactions. Inspired by cold Rydberg gases, where such disorder can be engineered usi… ▽ More Strongly interacting quantum systems subject to quenched disorder exhibit intriguing phenomena such as glassiness and many-body localization. Theoretical studies have mainly focused on disorder in the form of random potentials, while many experimental realizations naturally feature disorder in the interparticle interactions. Inspired by cold Rydberg gases, where such disorder can be engineered using the dipole blockade effect,we study a Heisenberg XXZ spin model where the disorder is exclusively due to random spin-spin couplings, arising from power-law interactions between randomly positioned spins. Using established spectral and eigenstate properties and entanglement entropy, we show that this system exhibits a localization crossover and identify strongly interacting pairs as emergent local conserved quantities in the system, leading to an intuitive physical picture consistent with our numerical results. △ Less

Submitted 21 November, 2022; v1 submitted 29 July, 2022; originally announced July 2022.

Comments: 10 pages, 6 main figures, 1 supplementary figure, close to published version

Journal ref: Phys. Rev. B 106, 134212 (2022)

Emergent pair localization in a many-body quantum spin system

Authors: Titus Franz, Sebastian Geier, Adrian Braemer, Clément Hainaut, Adrien Signoles, Nithiwadee Thaicharoen, Annika Tebben, André Salzinger, Martin Gärttner, Gerhard Zürn, Matthias Weidemüller

Abstract: Understanding how closed quantum systems dynamically approach thermal equilibrium presents a major unresolved problem in statistical physics. Generically, non-integrable quantum systems are expected to thermalize as they comply with the Eigenstate Thermalization Hypothesis. However, in the presence of strong disorder, the dynamics can possibly slow down to a degree that systems fail to thermalize… ▽ More Understanding how closed quantum systems dynamically approach thermal equilibrium presents a major unresolved problem in statistical physics. Generically, non-integrable quantum systems are expected to thermalize as they comply with the Eigenstate Thermalization Hypothesis. However, in the presence of strong disorder, the dynamics can possibly slow down to a degree that systems fail to thermalize on experimentally accessible timescales, as in spin glasses or many-body localized systems. In general, particularly in long-range interacting quantum systems, the specific nature of the disorder necessary for the emergence of a prethermal, metastable state--distinctly separating the timescales of initial relaxation and subsequent slow thermalization--remains an open question. We study an ensemble of Heisenberg spins with a tunable distribution of random coupling strengths realized by a Rydberg quantum simulator. We observe a drastic change in the late-time magnetization when increasing disorder strength. The data is well described by models based on pairs of strongly interacting spins, which are treated as thermal for weak disorder and isolated for strong disorder. Our results indicate a crossover into a pair-localized prethermal regime in a closed quantum system of thousands of spins in the critical case where the exponent of the power law interaction matches the spatial dimension. △ Less

Submitted 26 February, 2024; v1 submitted 28 July, 2022; originally announced July 2022.

Ultrafast Many-Body Dynamics in an Ultracold Rydberg-Excited Atomic Mott Insulator

Authors: V. Bharti, S. Sugawa, M. Mizoguchi, M. Kunimi, Y. Zhang, S. de Léséleuc, T. Tomita, T. Franz, M. Weidemüller, K. Ohmori

Abstract: We report the observation and control of ultrafast non-equilibrium many-body electron dynamics in Rydberg-excited spatially-ordered ultracold atoms created from a three-dimensional unity-filling atomic Mott insulator. By implementing time-domain Ramsey interferometry with attosecond precision in our Rydberg atomic system, we observe picosecond-scale ultrafast many-body dynamics that is essentially… ▽ More We report the observation and control of ultrafast non-equilibrium many-body electron dynamics in Rydberg-excited spatially-ordered ultracold atoms created from a three-dimensional unity-filling atomic Mott insulator. By implementing time-domain Ramsey interferometry with attosecond precision in our Rydberg atomic system, we observe picosecond-scale ultrafast many-body dynamics that is essentially governed by the emergence and evolution of many-body correlations between long-range interacting atoms in an optical lattice. We analyze our observations with different theoretical approaches and find that quantum fluctuations have to be included beyond semi-classical descriptions to describe the observed dynamics. Our Rydberg lattice platform combined with an ultrafast approach, which is robust against environmental noises, opens the door for simulating strongly-correlated electron dynamics by long-range van der Waals interaction and resonant dipole-dipole interaction to the charge-overlapping regime in synthetic ultracold atomic crystals. △ Less

Submitted 24 January, 2022; originally announced January 2022.

Journal ref: Phys. Rev. Lett. 131, 123201 (2023)

Microwave-engineering of programmable XXZ Hamiltonians in arrays of Rydberg atoms

Authors: P. Scholl, H. J. Williams, G. Bornet, F. Wallner, D. Barredo, T. Lahaye, A. Browaeys, L. Henriet, A. Signoles, C. Hainaut, T. Franz, S. Geier, A. Tebben, A. Salzinger, G. Zürn, M. Weidemüller

Abstract: We use the resonant dipole-dipole interaction between Rydberg atoms and a periodic external microwave field to engineer XXZ spin Hamiltonians with tunable anisotropies. The atoms are placed in 1D and 2D arrays of optical tweezers, allowing us to study iconic situations in spin physics, such as the implementation of the Heisenberg model in square arrays, and the study of spin transport in 1D. We fi… ▽ More We use the resonant dipole-dipole interaction between Rydberg atoms and a periodic external microwave field to engineer XXZ spin Hamiltonians with tunable anisotropies. The atoms are placed in 1D and 2D arrays of optical tweezers, allowing us to study iconic situations in spin physics, such as the implementation of the Heisenberg model in square arrays, and the study of spin transport in 1D. We first benchmark the Hamiltonian engineering for two atoms, and then demonstrate the freezing of the magnetization on an initially magnetized 2D array. Finally, we explore the dynamics of 1D domain wall systems with both periodic and open boundary conditions. We systematically compare our data with numerical simulations and assess the residual limitations of the technique as well as routes for improvements. The geometrical versatility of the platform, combined with the flexibility of the simulated Hamiltonians, opens exciting prospects in the field of quantum simulation, quantum information processing and quantum sensing. △ Less

Submitted 1 March, 2022; v1 submitted 30 July, 2021; originally announced July 2021.

Comments: 10 pages, 4 main figures, 2 supplementary figures

Journal ref: Phys. Rev. X Quantum vol. 3, p. 020303 (2022)

Semiclassical simulations predict glassy dynamics for disordered Heisenberg models

Authors: Philipp Schultzen, Titus Franz, Clément Hainaut, Sebastian Geier, Andre Salzinger, Annika Tebben, Gerhard Zürn, Martin Gärttner, Matthias Weidemüller

Abstract: We numerically study out-of-equilibrium dynamics in a family of Heisenberg models with $1/r^6$ power-law interactions and positional disorder. Using the semi-classical discrete truncated Wigner approximation (dTWA) method, we investigate the time evolution of the magnetization and ensemble-averaged single-spin purity for a strongly disordered system after initializing the system in an out-of-equil… ▽ More We numerically study out-of-equilibrium dynamics in a family of Heisenberg models with $1/r^6$ power-law interactions and positional disorder. Using the semi-classical discrete truncated Wigner approximation (dTWA) method, we investigate the time evolution of the magnetization and ensemble-averaged single-spin purity for a strongly disordered system after initializing the system in an out-of-equilibrium state. We find that both quantities display robust glassy behavior for almost any value of the anisotropy parameter of the Heisenberg Hamiltonian. Furthermore, a systematic analysis allows us to quantitatively show that, for all the scenarios considered, the stretch power lies close to the one analytically obtained in the Ising limit. This indicates that glassy relaxation behavior occurs widely in disordered quantum spin systems, independent of the particular symmetries and integrability of the Hamiltonian. △ Less

Submitted 28 July, 2021; originally announced July 2021.

Floquet Hamiltonian Engineering of an Isolated Many-Body Spin System

Authors: Sebastian Geier, Nithiwadee Thaicharoen, Clément Hainaut, Titus Franz, Andre Salzinger, Annika Tebben, David Grimshandl, Gerhard Zürn, Matthias Weidemüller

Abstract: Controlling interactions is the key element for quantum engineering of many-body systems. Using time-periodic driving, a naturally given many-body Hamiltonian of a closed quantum system can be transformed into an effective target Hamiltonian exhibiting vastly different dynamics. We demonstrate such Floquet engineering with a system of spins represented by Rydberg states in an ultracold atomic gas.… ▽ More Controlling interactions is the key element for quantum engineering of many-body systems. Using time-periodic driving, a naturally given many-body Hamiltonian of a closed quantum system can be transformed into an effective target Hamiltonian exhibiting vastly different dynamics. We demonstrate such Floquet engineering with a system of spins represented by Rydberg states in an ultracold atomic gas. Applying a sequence of spin manipulations, we change the symmetry properties of the effective Heisenberg XYZ Hamiltonian. As a consequence, the relaxation behavior of the total spin is drastically modified. The observed dynamics can be qualitatively captured by a semi-classical simulation. Synthesising a wide range of Hamiltonians opens vast opportunities for implementing quantum simulation of non-equilibrium dynamics in a single experimental setting. △ Less

Submitted 4 May, 2021; originally announced May 2021.

Glassy quantum dynamics of disordered Ising spins

Authors: Philipp Schultzen, Titus Franz, Sebastian Geier, Andre Salzinger, Annika Tebben, Clément Hainaut, Gerhard Zürn, Matthias Weidemüller, Martin Gärttner

Abstract: We study the out-of-equilibrium dynamics in the quantum Ising model with power-law interactions and positional disorder. For arbitrary dimension $d$ and interaction range $α\geq d$ we analytically find a stretched exponential decay of the global magnetization and ensemble-averaged single-spin purity with a stretch-power $β= d/α$ in the thermodynamic limit. Numerically, we confirm that glassy behav… ▽ More We study the out-of-equilibrium dynamics in the quantum Ising model with power-law interactions and positional disorder. For arbitrary dimension $d$ and interaction range $α\geq d$ we analytically find a stretched exponential decay of the global magnetization and ensemble-averaged single-spin purity with a stretch-power $β= d/α$ in the thermodynamic limit. Numerically, we confirm that glassy behavior persists for finite system sizes and sufficiently strong disorder. We identify dephasing between disordered coherent pairs as the main mechanism leading to a relaxation of global magnetization, whereas genuine many-body interactions lead to a loss of single-spin purity which signifies the build-up of entanglement. The emergence of glassy dynamics in the quantum Ising model extends prior findings in classical and open quantum systems, where the stretched exponential law is explained by a scale-invariant distribution of time scales, to both integrable and non-integrable quantum systems. △ Less

Submitted 29 July, 2021; v1 submitted 1 April, 2021; originally announced April 2021.

Depletion Imaging of Rydberg atoms in cold atomic gases

Authors: M. Ferreira-Cao, V. Gavryusev, T. Franz, R. Ferracini Alves, A. Signoles, G. Zürn, M. Weidemüller

Abstract: We present a depletion imaging technique to map out the spatial and temporal dependency of the density distribution of an ultracold gas of Rydberg atoms. Locally resolved absorption depletion, observed through differential ground state absorption imaging of a $^{87}\text{Rb}$ cloud in presence and absence of pre-excited Rydberg atoms, reveals their projected two-dimensional distribution. By employ… ▽ More We present a depletion imaging technique to map out the spatial and temporal dependency of the density distribution of an ultracold gas of Rydberg atoms. Locally resolved absorption depletion, observed through differential ground state absorption imaging of a $^{87}\text{Rb}$ cloud in presence and absence of pre-excited Rydberg atoms, reveals their projected two-dimensional distribution. By employing a closed two-level optical transition uncoupled from the Rydberg state, the highly excited atoms are preserved during imaging. We measure the excitation dynamics of the $\vert48S\rangle$ state of $^{87}\text{Rb}$, observing a saturation of the two-dimensional Rydberg density. Such outcome can be explained by the Rydberg blockade effect which prevents resonant excitation of close-by Rydberg atoms due to strong dipolar interactions. By combining the superatom description, where atoms within a blockade radius are represented as collective excitations, with a Monte Carlo sampling, we can quantitatively model the observed excitation dynamics and infer the full three-dimensional distribution of Rydberg atoms, that can serve as a starting point for quantum simulation of many-body dynamics involving Rydberg spin systems. △ Less

Submitted 28 July, 2020; v1 submitted 14 November, 2019; originally announced November 2019.

Comments: 12 pages, 3 figures

Journal ref: J. Phys. B: At. Mol. Opt. Phys. 53 084004 (2020)

Glassy dynamics in a disordered Heisenberg quantum spin system

Authors: A. Signoles, T. Franz, R. Ferracini Alves, M. Gärttner, S. Whitlock, G. Zürn, M. Weidemüller

Abstract: Understanding the dynamics of strongly interacting disordered quantum systems is one of the most challenging problems in modern science, due to features such as the breakdown of thermalization and the emergence of glassy phases of matter. We report on the observation of anomalous relaxation dynamics in an isolated XXZ quantum spin system realized by an ultracold gas of atoms initially prepared in… ▽ More Understanding the dynamics of strongly interacting disordered quantum systems is one of the most challenging problems in modern science, due to features such as the breakdown of thermalization and the emergence of glassy phases of matter. We report on the observation of anomalous relaxation dynamics in an isolated XXZ quantum spin system realized by an ultracold gas of atoms initially prepared in a superposition of two-different Rydberg states. The total magnetization is found to exhibit sub-exponential relaxation analogous to classical glassy dynamics, but in the quantum case this relaxation originates from the build-up of non-classical correlations. In both experiment and semi-classical simulations, we find the evolution towards a randomized state is independent of the strength of disorder up to a critical value. This hints towards a unifying description of relaxation dynamics in disordered isolated quantum systems, analogous to the generalization of statistical mechanics to out-of-equilibrium scenarios in classical spin glasses. △ Less

Submitted 3 December, 2020; v1 submitted 26 September, 2019; originally announced September 2019.

Journal ref: Phys. Rev. X 11, 011011 (2021)

Space-borne Bose-Einstein condensation for precision interferometry

Authors: Dennis Becker, Maike D. Lachmann, Stephan T. Seidel, Holger Ahlers, Aline N. Dinkelaker, Jens Grosse, Ortwin Hellmig, Hauke Müntinga, Vladimir Schkolnik, Thijs Wendrich, André Wenzlawski, Benjamin Weps, Robin Corgier, Daniel Lüdtke, Tobias Franz, Naceur Gaaloul, Waldemar Herr, Manuel Popp, Sirine Amri, Hannes Duncker, Maik Erbe, Anja Kohfeldt, André Kubelka-Lange, Claus Braxmaier, Eric Charron , et al. (10 additional authors not shown)

Abstract: Space offers virtually unlimited free-fall in gravity. Bose-Einstein condensation (BEC) enables ineffable low kinetic energies corresponding to pico- or even femtokelvins. The combination of both features makes atom interferometers with unprecedented sensitivity for inertial forces possible and opens a new era for quantum gas experiments. On January 23, 2017, we created Bose-Einstein condensates i… ▽ More Space offers virtually unlimited free-fall in gravity. Bose-Einstein condensation (BEC) enables ineffable low kinetic energies corresponding to pico- or even femtokelvins. The combination of both features makes atom interferometers with unprecedented sensitivity for inertial forces possible and opens a new era for quantum gas experiments. On January 23, 2017, we created Bose-Einstein condensates in space on the sounding rocket mission MAIUS-1 and conducted 110 experiments central to matter-wave interferometry. In particular, we have explored laser cooling and trapping in the presence of large accelerations as experienced during launch, and have studied the evolution, manipulation and interferometry employing Bragg scattering of BECs during the six-minute space flight. In this letter, we focus on the phase transition and the collective dynamics of BECs, whose impact is magnified by the extended free-fall time. Our experiments demonstrate a high reproducibility of the manipulation of BECs on the atom chip reflecting the exquisite control features and the robustness of our experiment. These properties are crucial to novel protocols for creating quantum matter with designed collective excitations at the lowest kinetic energy scales close to femtokelvins. △ Less

Submitted 18 June, 2018; originally announced June 2018.

Comments: 6 pages, 4 figures

Journal ref: Nature 562, 391-395 (2018)