Quantum Physics · Cross-listed from cond-mat.mes-hall
Anisotropic transport in ballistic bilayer graphene cavities
Florian Schoeppl, Alina Mrenca-Kolasinska, Ming-Hao Liu et al. (+3 more)
Closing the gap between ray tracing simulations and experimentally observed electron jetting in
bilayer graphene (BLG), we study all-electronic, gate-defined BLG cavities using tight-binding simulations and semiclassical equations of motion. Such cavities offer a rich playground to investigate anisotropic electron transport due to the trigonally warped
Fermi surfaces. In this work, we achieve two things: First, we verify the existence of triangular modes (as predicted by classical ray tracing calculations) in the
quantum solutions of closed circular BLG cavities. Then, we explore signatures of said triangular modes in transport through open BLG cavities connected to leads. We show that the triangular
symmetry translates into anisotropic transport and present an optimal setup for experimental detection of the triangular modes as well as for controlled modulation of transport in preferred directions.
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All authors Florian Schoeppl, Alina Mrenca-Kolasinska, Ming-Hao Liu, Korbinian Schwarzmaier, Klaus Richter, Angelika Knothe
Quantum Physics · Cross-listed from gr-qc
Radiative process of tripartite entangled probes in inertial motion
Subhajit Barman and K. Hari
We study the radiative process of three entangled
quantum probes initially prepared in a tripartite W state. As a basic set-up, we consider the probes to be inertial in flat spacetime and investigate how the radiative process is affected by different probe configurations. We take the
quantum probes as either static or moving with uniform velocities and consider different switching scenarios. Our main observation confirms that the radiative process depends distinctively on the initial configuration in which the probes are arranged, as well as on the direction of the probe velocity. We also extend our analysis to a thermal environment, thereby simulating a more realistic background. We thoroughly discuss the effects due to different switchings, the thermal background, and probe motion on the radiative process of these tripartite entangled probes. We also comment on how the observations from this work can help prepare a set-up least affected by
quantum decoherence.
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Quantum Physics
D.-S. Wang, X. Xu and Y.-D. Liu
The notion of “picture” is fundamental in
quantum mechanics. In this work, a new picture, which we call
entanglement picture, is proposed based on the novel channel-state duality, whose importance is revealed in
quantum information science. We illustrate the application of
entanglement picture in
quantum algorithms for the simulation of many-body dynamics,
quantum field theory, thermal physics, and more generic quantities.
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Quantum Physics
Tunable passive squeezing of squeezed light through unbalanced double homodyne detection
Niels Tripier-Mondancin, David Barral, Ganaël Roeland et al. (+3 more)
The full characterization of
quantum states of light is a central task in
quantum optics and information science. Double homodyne detection provides a powerful method for the direct measurement of the Husimi Q quasi-probability distribution, offering a complete state representation in a simple experimental setting and a limited time frame. Here, we demonstrate that double homodyne detection can serve as more than a passive characterization tool. By intentionally unbalancing the input beamsplitter that splits the
quantum signal, we show that the detection scheme itself performs an effective squeezing or anti-squeezing transformation on the state being measured. The resulting measurement directly samples the Q function of the input state as if it were acted upon by a squeezing operator whose strength is a tunable experimental parameter: the beamsplitter's reflectivity. We experimentally realize this technique using a robust polarization-encoded double homodyne detection to characterize a squeezed
vacuum state. Our results demonstrate the controlled deformation of the measured Q function's phase-space distribution, confirming that unbalanced double homodyne detection is a versatile tool for simultaneous
quantum state manipulation and characterization.
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All authors Niels Tripier-Mondancin, David Barral, Ganaël Roeland, Raúl Leonardo Rincon Celis, Yann Bouchereau, Nicolas Treps
Quantum Physics
Syntactic Structure, Quantum Weights
Kentaro Imafuku
Why do local actions and exponential Euclidean weights arise so universally in classical, statistical, and
quantum theories? We offer a structural explanation from minimal constraints on finite descriptions of admissible histories. Assume that histories admit finite, self-delimiting (prefix-free) generative codes that can be decoded sequentially in a single forward pass. These purely syntactic requirements define a minimal descriptive cost, interpretable as a smoothed minimal program length, that is additive over local segments. First, any continuous local additive cost whose stationary sector coincides with the empirically identified classical variational sector is forced into a unique Euler–Lagrange equivalence class. Hence the universal form of an action is fixed by descriptional structure alone, while the specific microscopic Lagrangian and couplings remain system-dependent semantic input. Second, independently of microscopic stochasticity, finite prefix-free
languages exhibit exponential redundancy: many distinct programs encode the same coarse history, and this redundancy induces a universal exponential multiplicity weight on histories. Requiring this weight to be real and bounded below selects a real Euclidean representative for stable local bosonic systems, yielding the standard Euclidean path-integral form. When Osterwalder–Schrader reflection positivity holds, the Euclidean measure reconstructs a
unitary Lorentzian amplitude.
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Quantum Physics
Higher Josephson harmonics in a tunable double-junction transmon qubit
Ksenia Shagalov, David Feldstein-Bofill, Leo Uhre Jakobsen et al. (+11 more)
Tunable Josephson harmonics open new avenues for
qubit design. We demonstrate a superconducting
circuit element consisting of a tunnel junction in series with a SQUID loop, yielding a Josephson potential whose harmonic content is strongly tunable by
magnetic flux. Through spectroscopy of the first four
qubit transitions, together with an effective single-mode model renormalized by the internal mode, we resolve a second harmonic with an amplitude up to $\sim10\%$ of the fundamental. We identify a flux sweet spot where the dispersive shift vanishes, achieved by balancing the dispersive couplings to the internal and
qubit modes. This highly tunable element provides a route toward protected
qubits and customizable nonlinear microwave devices.
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All authors Ksenia Shagalov, David Feldstein-Bofill, Leo Uhre Jakobsen, Zhenhai Sun, Casper Wied, Amalie T. J. Paulsen, Johann Bock Severin, Malthe A. Marciniak, Clinton A. Potts, Anders Kringhøj, Jacob Hastrup, Karsten Flensberg, Svend Krøjer, Morten Kjaergaard
Quantum Physics
Heralded generation of a three-mode NOON state
Sukhjit P. Singh, Elnaz Bazzazi, Diego N. Bernal-García et al. (+8 more)
Entangled states of
photons form the foundation of
quantum communication, computation, and metrology. Yet their generation remains fundamentally constrained: in the absence of intrinsic
photon-
photon interactions, the generation of such states is inherently probabilistic rather than deterministic. The prevalent technique of post-selection verifies the creation of an entangled state by detecting and thus destroying it. Heralding offers a solution in which measuring ancillary
photons in auxiliary modes signals the state generation without the need to measure it. Here, we introduce and experimentally demonstrate a scheme to generate a three-mode two-
photon NOON state, where the detection of a single
photon in one heralding mode signifies the presence of the state in three target modes. We validate the generated state by estimating a fidelity of 0.823 +/- 0.018 with respect to an ideal three-mode NOON state and certifying genuine multipartite
entanglement. By virtue of the high success probability and small resource overhead of our scheme, our work provides a theoretical and experimental stepping stone for entangled multi-mode state generation, which is realizable with current technology. These multi-mode entangled states represent a key direction for linear optical
quantum information that is complementary to multi-
qubit state encoding.
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All authors Sukhjit P. Singh, Elnaz Bazzazi, Diego N. Bernal-García, Simon White, Hassan Jamal Latief, Alison Goldingay, Sven Rogge, Sergei Slussarenko, Farzad Ghafari, Emanuele Polino, Nora Tischler
Quantum Physics
Generation of high-OAM ultraviolet twisted light for RF-photoinjector applications
A.S. Dyatlov, D.M. Dolgintsev, V.V. Gerasimov et al. (+7 more)
The generation of relativistic
vortex electron beams via photoemission requires ultraviolet
laser beams with well-controlled orbital angular momentum (OAM) and compatibility with
radio-frequency (RF) photoinjector drive-
laser systems. High-OAM
vortex beams at a wavelength of 266 nm are generated using three fabricated diffractive optical elements integrated into an operational photoinjector beamline: a reflective fork grating, a high-topological-charge spiral phase plate, and binary axicons. The spiral phase plate produces a high-purity Laguerre-Gaussian mode with an OAM of l = 64 and a conversion efficiency of 80%, whereas binary axicons generate low-divergence quasi-Bessel beams forming a superposition of multiple OAM states with a finite OAM bandwidth imposed by their binary phase structure. Fork gratings provide flexible access to lower OAM values and enable robust modal diagnostics. The generated beams are characterized using cylindrical-lens mode conversion and radial intensity analysis, demonstrating practical control of both the OAM content and spectral bandwidth of ultraviolet structured light for accelerator-based applications.
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All authors A.S. Dyatlov, D.M. Dolgintsev, V.V. Gerasimov, V.V. Kobets, V.P. Nazmov, M.A. Nozdrin, A.N. Sergeev, D.S. Shokin, K.E. Yunenko, D.V. Karlovets
Quantum Physics
Benchmarking Gaussian and non-Gaussian input states with a hybrid sampling platform
Michael Stefszky, Kai-Hong Luo, Jan-Lucas Eickmann et al. (+22 more)
The original
boson sampling paradigm-consisting of multiple single-
photon input states, a large interferometer, and multi-channel click detection-was originally proposed as a photonic route to
quantum computational advantage. Its non-Gaussian resources, essential for outperforming any classical system, are provided by single-
photon inputs and click detection. Yet the drive toward larger experiments has led to the replacement of experimentally demanding single-
photon sources with Gaussian states, thereby diminishing the available non-Gaussianity-a critical
quantum resource. As the community broadens its focus from the initial sampling task to possible real-world applications, it becomes crucial to quantify the performance cost associated with reducing non-Gaussian resources and to
benchmark sampling platforms that employ different input states. To address this need, we introduce the Paderborn
Quantum Sampler (PaQS), a hybrid platform capable of performing sampling experiments with eight Gaussian or non-Gaussian input states in a 12-mode interferometer within a single experimental run. This architecture enables direct, side-by-side benchmarking of distinct sampling regimes under otherwise identical conditions. By employing a semi-device-independent framework, offering certification that does not rely on prior knowledge of the interferometer or the input states, we verify that the observed data cannot be reproduced by any classical model-a prerequisite for demonstrating
quantum advantage. Applying this framework, we observe clear performance gains arising from non-Gaussian input states.
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All authors Michael Stefszky, Kai-Hong Luo, Jan-Lucas Eickmann, Simone Atzeni, Florian Lütkewitte, Cheeranjiv Pandey, Fabian Schlue, Jonas Lammers, Mikhail Roiz, Timon Schapeler, Laura Ares, Milad Yahyapour, Alexander Kastner, Joschua Martinek, Michael Mittermair, Carlos Sevilla-Gutiérrez, Marius Leyendecker, Oskar Kohout, Dmitriy Mitin, Ronald Holzwarth, Jan Sperling, Tim Bartley, Fabian Steinlechner, Benjamin Brecht, Christine Silberhorn
Quantum Physics
Zhijian Lai, Dong An, Jiang Hu et al. (+1 more)
Grover's
algorithm is a fundamental
quantum algorithm that offers a quadratic speedup for the unstructured search problem by alternately applying physically implementable oracle and
diffusion operators. In this paper, we reformulate the unstructured search as a maximization problem on the
unitary manifold and solve it via the Riemannian gradient ascent (RGA) method. To overcome the difficulty that generic RGA updates do not, in general, correspond to physically implementable
quantum operators, we introduce Grover-compatible retractions to restrict RGA updates to valid oracle and
diffusion operators. Theoretically, we establish a local Riemannian $\mu$-Polyak-Łojasiewicz (PL) inequality with $\mu = \tfrac{1}{2}$, which yields a linear convergence rate of $1 - \kappa^{-1}$ toward the global solution. Here, the condition number $\kappa = L_{\mathrm{Rie}} / \mu$, where $L_{\mathrm{Rie}}$ denotes the Riemannian Lipschitz constant of the gradient. Taking into account both the geometry of the
unitary manifold and the special structure of the cost function, we show that $L_{\mathrm{Rie}} = O(\sqrt{N})$ for problem size $N = 2^n$. Consequently, the resulting iteration complexity is $O(\sqrt{N} \log(1/\varepsilon))$ for attaining an $\varepsilon$-accurate solution, which matches the quadratic speedup of $O(\sqrt{N})$ achieved by Grover's
algorithm. These results demonstrate that an optimization-based viewpoint can offer fresh conceptual insights and lead to new advances in the design of
quantum algorithms.
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All authors Zhijian Lai, Dong An, Jiang Hu, Zaiwen Wen
Quantum Physics
Real-time heralded non-Gaussian teleportation resource-state generator
Joseph C. Chapman, Yanbao Zhang, Joseph M. Lukens et al. (+4 more)
Quantum teleportation is a fundamental
quantum communications primitive that requires an entangled resource state. In the continuous-variable regime, non-Gaussian entangled resources have been shown theoretically to improve teleportation fidelity compared to Gaussian squeezed
vacuum. We experimentally demonstrate a heralded two-mode resource state for non-Gaussian teleportation capable of real-time use. We characterize this state with two-mode homodyne
tomography showing it has fidelity $F=0.973\pm 0.005$ with the expected resource state. Real-time use is enabled by a
photon-subtraction orchestrator system performing live coincidence detection and outputting low-jitter and low-latency heralding signals. Live collection of real-time quadrature measurements of
photon-subtracted states is enabled by the development of a synchronized homodyne detection server, where the orchestrator system queries the server to collect the real-time quadrature samples corresponding to the heralded state. These results demonstrate significant advancement in enabling the use of heralded non-Gaussian states in
quantum networking protocols, especially in the context of
quantum repeaters, non-Gaussian
quantum sensing, and measurement-based
quantum computing.
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All authors Joseph C. Chapman, Yanbao Zhang, Joseph M. Lukens, Alberto M. Marino, Eugene Dumitrescu, Yan Wang, Nicholas A. Peters
Quantum Physics · Cross-listed from cond-mat.str-el
Decay of spin helices in XXZ quantum spin chains with single-ion anisotropy
Florian Lange, Frank Göhmann, Gerhard Wellein et al. (+1 more)
Long-lived
spin-helix states facilitate the study of non-
equilibrium dynamics in
quantum magnets. We consider the decay of transverse
spin-helices in
antiferromagnetic spin-$S$ XXZ chains with single-ion anisostropy. The
spin-helix decay is observable in the time
evolution of the local magnetization that we calculate numerically for the system in the thermodynamic limit using infinite time-evolving block decimation simulations. Although the single-ion anisotropy prevents helix states from being eigenstates of the
Hamiltonian, they still can be long-lived for appropriately chosen wave numbers. In case of an easy-axis exchange anisotropy the single-ion anisotropy may even stabilize the helices. Within a
spin-wave approximation, we obtain a condition giving an estimate for the most stable wave number $Q$ that agrees qualitatively with our numerical results.
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All authors Florian Lange, Frank Göhmann, Gerhard Wellein, Holger Fehske
Quantum Physics
Universal recoverability of quantum states in tracial von-Neumann algebras
Saptak Bhattacharya
In this paper, we discuss a refinement of
quantum data processing inequality for the sandwiched quasi-relative
entropy $\mathcal{S}_2$ on a tracial von-Neumann
algebra. The main result is a universal recoverability bound with the Petz recovery map, which was previously obtained in the finite dimensional setup.
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Quantum Physics
Single-step phase-engineered pulse for active readout cavity reset with a known qubit state
Ren-Ze Zhao, Ze-An Zhao, Tian-Le Wang et al. (+9 more)
In a
circuit QED architecture, we experimentally demonstrate a hardware-efficient and
qubit-state-dependent Single-Step Phase-Engineered (SSPE) pulse scheme for actively depopulating a readout cavity. The protocol appends a reset segment with tailored amplitude and phase to a square readout pulse. Within the linear-response regime, the optimal reset amplitude scales proportionally with the readout amplitude, while the optimal reset phase remains invariant, significantly simplifying the experimental calibration procedure. For a known
qubit state, time-resolved measurements demonstrate that the SSPE pulse achieves faster cavity depletion than the CLEAR protocol. Crucially, this approach enables arbitrarily fast, overshoot-free depletion of the cavity
photon population, with the ultimate reset rate constrained by the available drive amplitude and the finite analog bandwidth of the measurement chain. A comprehensive evaluation of the QND character reveals no measurable increase in non-QNDness relative to the free-decay and CLEAR protocols. The remaining non-QNDness is predominantly attributable to state switching induced by
qubit relaxation during the readout process. These results establish the SSPE scheme as a practical and scalable approach for achieving rapid and smooth cavity reset in superconducting
quantum circuits in the case of a known
qubit state.
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All authors Ren-Ze Zhao, Ze-An Zhao, Tian-Le Wang, Peng Wang, Sheng Zhang, Xiao-Yan Yang, Hai-Feng Zhang, Zhi-Fei Li, Yuan Wu, Sheng-Ri Liu, Peng Duan, Guo-Ping Guo
Quantum Physics
Practical protein-pocket hydration-site prediction for drug discovery on a quantum computer
Daniele Loco, Kisa Barkemeyer, Andre R. R. Carvalho et al. (+1 more)
Demonstrating the practical utility of Noisy Intermediate-Scale
Quantum (NISQ) hardware for recurrent tasks in Computer-Aided Drug Discovery is of paramount importance. We tackle this challenge by performing three-dimensional
protein pockets hydration-site prediction on a
quantum computer. Formulating the water placement problem as a Quadratic Unconstrained Binary Optimization (QUBO), we use a hybrid approach coupling a classical three-dimensional reference-interaction site model (3D-RISM) to an efficient
quantum optimization solver, to run various hardware experiments up to 123
qubits. Matching the precision of classical approaches, our results reproduced experimental predictions on real-life
protein-ligand complexes. Furthermore, through a detailed resource estimation analysis, we show that accuracy can be systematically improved with increasing number of
qubits, indicating that full
quantum utility is in reach. Finally, we provide evidence that advantageous situations could be found for systems where classical optimization struggles to provide optimal solutions. The method has potential for assisting simulations of
protein-ligand complexes for drug lead optimization and setup of docking calculations.
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All authors Daniele Loco, Kisa Barkemeyer, Andre R. R. Carvalho, Jean-Philip Piquemal
Quantum Physics
Constraint-oriented biased quantum search for general constrained combinatorial optimization problems
Sören Wilkening
We present a
quantum algorithmic routine that extends the realm of Grover-based heuristics for tackling combinatorial optimization problems with arbitrary efficiently computable objective and constraint functions. Building on previously developed
quantum methods that were primarily restricted to linear constraints, we generalize the approach to encompass a broader class of problems in discrete domains. To evaluate the potential of our
algorithm, we assume the existence of sufficiently advanced logical
quantum hardware. With this assumption, we demonstrate that our method has the potential to outperform state-of-the-art classical solvers and heuristics in terms of both runtime scaling and solution quality. The same may be true for more realistic implementations, as the logical
quantum algorithm can achieve runtime savings of up to $10^2-10^3$.
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Quantum Physics
Deterministic Quantum Communication Between Fixed-Frequency Superconducting Qubits via Broadband Resonators
Takeaki Miyamura, Zhiling Wang, Kohei Matsuura et al. (+5 more)
Quantum communication between remote chips is essential for realizing large-scale superconducting
quantum computers. For such communication, itinerant microwave
photons propagating through transmission lines offer a promising approach. However, demonstrations to date have relied on frequency-tunable
circuit elements to compensate for fabrication-related parameter variations between sender and receiver devices, introducing control complexity and limiting scalability. In this work, we demonstrate deterministic
quantum state transfer and remote
entanglement generation between fixed-frequency superconducting
qubits on separate chips. To compensate for the sender-receiver mismatch, we employ a frequency-tunable
photon-generation technique which enables us to adjust the
photon frequency without modifying
circuit parameters. To enhance the frequency tunability, we implement broadband transfer resonators composed of two coupled coplanar-waveguide resonators, achieving a bandwidth of more than 100 MHz. This broadband design enables successful
quantum communication across a 30-MHz range of
photon frequencies between the remote
qubits.
Quantum process
tomography reveals state transfer fidelities of around 79% and Bell-state fidelities of around 73% across the full frequency range. Our approach avoids the complexity of the control lines and noise channels, providing a flexible pathway toward scalable
quantum networks.
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All authors Takeaki Miyamura, Zhiling Wang, Kohei Matsuura, Yoshiki Sunada, Keika Sunada, Kenshi Yuki, Jesper Ilves, Yasunobu Nakamura
Quantum Physics
Photonic Quantum-Accelerated Machine Learning
Markus Rambach, Abhishek Roy, Alexei Gilchrist et al. (+4 more)
Machine learning is widely applied in modern society, but has yet to capitalise on the unique benefits offered by
quantum resources.
Boson sampling – a
quantum-interference based sampling protocol – is a resource that is classically hard to simulate and can be implemented on current
quantum hardware. Here, we present a
quantum accelerator for classical machine learning, using
boson sampling to provide a high-dimensional
quantum fingerprint for reservoir computing. We show robust performance improvements under various conditions: imperfect
photon sources down to complete distinguishability; scenarios with severe class imbalances, classifying both handwritten digits and biomedical images; and sparse data, maintaining model accuracy with twenty times less training data. Crucially, we demonstrate the acceleration of our scheme on a photonic
quantum processing unit, providing experimental validation that
boson-sampling-enhanced learning with Fock states delivers real performance gains on actual
quantum hardware.
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All authors Markus Rambach, Abhishek Roy, Alexei Gilchrist, Akitada Sakurai, William J. Munro, Kae Nemoto, Andrew G. White
Quantum Physics
Quantum-classical correspondence in resonant and nonresonant Rabi-Stark model
Shangyun Wang, Songbai Chen and Jiliang Jing
Testing the correspondence principle in nonlinear
quantum systems is a fundamental pursuit in
quantum physics. In this paper, we employed mean field approximation theory to study the semiclassical dynamics in the Rabi-Stark model (RSM) and showed that the nonlinear Stark coupling significantly modulates the semiclassical phase space structure. By analyzing the linear
entanglement entropy of coherent states prepared in the classical chaotic and regular regions of the semiclassical phase space, we demonstrate that
quantum-classical correspondence can be achieved in the RSM with large atom-light frequency ratios. While this correspondence fails in the resonant Rabi model because its truncated
photon number is insufficient to approach the large
quantum number limit, we discovered that in the resonant RSM when the nonlinear Stark coupling $U \to \pm 1$, the time-averaged linear
entanglement entropy correlates strongly with the semiclassical phase space. In particular, when $U \to -1$, the truncated
photon number in the resonant RSM is very close to that in the resonant Rabi model, but the time-averaged linear
entanglement entropy still corresponds well with the semiclassical phase space. This result demonstrates that
quantum-classical correspondence can be realized in the few-body resonant RSM.
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Quantum Physics
Discovering novel quantum dynamics with NISQ simulators
Pedram Roushan and Leigh S. Martin
Major technological advances of the past century are rooted in our understanding of
quantum physics in the non-interacting limit. A central challenge today is to understand the behavior of complex
quantum many-body systems, where interactions play an essential role. About four decades ago, Richard Feynman proposed using controllable
quantum systems to efficiently simulate complex physics and chemistry problems, envisioning
quantum orreries, highly tunable
quantum devices built to emulate less understood
quantum systems. Here we ask whether
quantum simulators have already uncovered new physical phenomena-and, if so, in which areas and with what impact. We find that, in several notable instances, they have advanced our understanding of many-body
quantum dynamics. Although many of these insights could in principle have been obtained theoretically or numerically, they were nevertheless first achieved using
quantum processors. While a broad landscape of problems beyond non-
equilibrium dynamics still awaits exploration, it is encouraging that
quantum simulators are already beginning to challenge and refine our conventional wisdom.
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Quantum Physics
Programmable Open Quantum Systems
Mingrui Jing, Mengbo Guo, Lin Zhu et al. (+2 more)
Programmability is a unifying paradigm for enacting families of
quantum transformations via fixed processors and program states, with a fundamental role and broad impact in
quantum computation and control. While there has been a shift from viewing open systems solely as a source of error to treating them as a computational resource, their programmability remains largely unexplored. In this work, we develop a framework that characterizes and quantifies the programmability of Lindbladian
semigroups by combining physically implementable
retrieval maps with time varying program states. Within this framework, we identify
quantum programmable classes enabled by
symmetry and
stochastic structure, including covariant
semigroups and fully dissipative Pauli Lindbladians with finite program dimension. We further provide a necessary condition for physical programmability that rules out coherent generators and typical dissipators generating amplitude damping. For such nonphysically programmable cases, we construct explicit protocols with finite resources. Finally, we introduce an operational programming cost, defined via the number of samples required to program the Lindbladian, and establish its core structural properties, such as continuity and faithfulness. These results provide a notion of programming cost for Lindbladians, bridge programmable channel theory and open system dynamics, and yield
symmetry driven compression schemes and actionable resource estimates for
semigroup simulation and control in noisy
quantum technologies.
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All authors Mingrui Jing, Mengbo Guo, Lin Zhu, Hongshun Yao, Xin Wang
Quantum Physics
Utility of noiseless linear amplification and attenuation in single-rail discrete-variable quantum communications
Ozlem Erkilic, Aritra Das, Angela A. Baiju et al. (+3 more)
Quantum communication offers many applications, with teleportation and superdense coding being two of the most fundamental. In these protocols, pre-shared
entanglement enables either the faithful transfer of
quantum states or the transmission of more information than is possible classically. However, channel losses degrade the shared states, reducing teleportation fidelity and the information advantage in superdense coding. Here, we investigate how to mitigate these effects by optimising the measurements applied by the communicating parties. We formulate the problem as an optimisation over general positive operator-valued measurements (POVMs) and compare the results with physically realisable noiseless attenuation (NA) and noiseless linear amplification (NLA)
circuits. For teleportation, NLA/NA and optimised POVMs improve the average fidelity by up to 78% while maintaining feasible success probabilities. For superdense coding, they enhance the
quantum advantage over the classical channel capacity by more than 100% in some regimes and shift the break-even point, thereby extending the tolerable range of losses. Notably, the optimal POVMs effectively reduce to NA or NLA, showing that simple, experimentally accessible operations already capture the essential performance gains.
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All authors Ozlem Erkilic, Aritra Das, Angela A. Baiju, Nicholas Zaunders, Biveen Shajilal, Timothy C. Ralph
Quantum Physics · Cross-listed from cond-mat.quant-gas
Direct Generation of an Array with 78400 Optical Tweezers Using a Single Metasurface
Yuqing Wang, Yuxuan Liao, Tao Zhang et al. (+9 more)
Scalability remains a major challenge in building practical fault-tolerant
quantum computers. Currently, the largest number of
qubits achieved across leading
quantum platforms ranges from hundreds to thousands. In atom arrays, scalability is primarily constrained by the capacity to generate large numbers of optical tweezers, and conventional techniques using acousto-optic deflectors or spatial light modulators struggle to produce arrays much beyond $\sim 10,000$ tweezers. Moreover, these methods require additional microscope objectives to focus the light into micrometer-sized spots, which further complicates system integration and scalability. Here, we demonstrate the experimental generation of an optical tweezer array containing $280\times 280$ spots using a metasurface, nearly an order of magnitude more than most existing systems. The metasurface leverages a large number of subwavelength phase-control pixels to engineer the wavefront of the incident light, enabling both large-scale tweezer generation and direct focusing into micron-scale spots without the need for a microscope. This result shifts the scalability bottleneck for atom arrays from the tweezer generation hardware to the available
laser power. Furthermore, the array shows excellent intensity uniformity exceeding $90\%$, making it suitable for homogeneous single-atom loading and paving the way for trapping arrays of more than $10,000$ atoms in the near future.
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All authors Yuqing Wang, Yuxuan Liao, Tao Zhang, Ye Tian, Yujia Wu, Wenjun Zhang, Wei Zhang, Yidong Huang, Hui Zhai, Wenlan Chen, Xue Feng, Zhongchi Zhang
Quantum Physics
Large-scale Lindblad learning from time-series data
Ewout van den Berg, Brad Mitchell, Ken Xuan Wei et al. (+1 more)
Learned open-
quantum-system models have broad applications in device characterization, device calibration, realistic noise model construction, and bounding observable estimates in
quantum simulation. To this end, we develop a highly scalable Lindblad learning protocol assuming an effective time-independent Lindblad generator with local interactions. For a given operation that can be applied repeatedly on a
quantum computer, the protocol learns the Lindbladian by forming a linear system of equations for the model parameters in terms of a set of observable values and their gradients. The required gradient information is obtained by fitting time-series data with sums of exponentially damped sinusoids and differentiating those curves. We develop a robust curve-fitting procedure that finds a parsimonious representation of the data up to shot noise. We demonstrate the approach by learning the Lindbladian for a full layer of gates on a 156-
qubit superconducting
quantum processor, providing the first learning experiment of this kind. We study the effects of state-preparation and measurement errors and limitations on the operations that can be learned. For improved performance under readout errors, we propose an optional fine-tuning strategy that improves the fit between the time-evolved model and the measured data.
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All authors Ewout van den Berg, Brad Mitchell, Ken Xuan Wei, Moein Malekakhlagh
Quantum Physics · Cross-listed from cond-mat.mes-hall
Device/circuit simulations of silicon spin qubits based on a gate-all-around transistor
Tetsufumi Tanamoto and Keiji Ono
We theoretically investigated the readout process of a
spin–
qubit structure based on a gate-all-around (GAA) transistor. Our study focuses on a logical
qubit composed of two physical
qubits. Different
spin configurations result in different charge distributions, which subsequently influence the electrostatic effects on the GAA transistor. Consequently, the current flowing through the GAA transistor depends on the
qubit's state. We calculated the current-voltage characteristics of the three-dimensional configurations of the
qubit and GAA structures, using technology computer-aided design (TCAD) simulations. Moreover, we performed
circuit simulations using the Simulation Program with Integrated
Circuit Emphasis (SPICE) to investigate whether a readout
circuit made from complementary metal–
oxide semiconductor (CMOS) transistors can amplify the weak signals generated by the
qubits. Our findings indicate that, by dynamically controlling the applied voltage within a properly designed
circuit, the readout can be detected effectively based on a conventional sense amplifier.
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Quantum Physics
Detecting quantum many-body states with imperfect measuring devices
K. Uriostegui, C. Pineda, C. Chryssomalakos et al. (+2 more)
We study a coarse-graining map arising from incomplete and imperfect addressing of particles in a multipartite
quantum system. In its simplest form, corresponding to a two-
qubit state, the resulting channel produces a convex mixture of the two partial traces. We derive the probability density of obtaining a given coarse-grained state, using
geometric arguments for two
qubits coarse-grained to one, and random-
matrix methods for larger systems. As the number of
qubits increases, the probability density sharply concentrates around the maximally mixed state, making nearly pure coarse-grained states increasingly unlikely. For two
qubits, we also compute the inverse state needed to characterize the effective dynamics under coarse-graining and find that the average preimage of the maximally mixed state contains a finite singlet component. Finally, we validate the analytical predictions by inferring the underlying probabilities from Monte-Carlo-generated coarse-grained statistics.
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All authors K. Uriostegui, C. Pineda, C. Chryssomalakos, V. Rascón Barajas, I. Vázquez Mota
Quantum Physics
The strength of weak coupling
Alastair Kay and Christino Tamon
A paradoxical idea in
quantum transport is that attaching weakly-coupled edges to a large base graph creates high-fidelity
quantum state transfer. We provide a mathematical treatment that rigorously prove this folklore idea. Our proofs are elementary and build upon the Feshbach-Schur method from perturbation theory. We also show the idea is effective in circumventing Anderson localization in
spin chains and finding speedups in hitting times useful for
quantum search.
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