Quantum Physics
Optimal cloning of mixed states
Marco Fanizza, Dmitry Grinko, Thilo Scharnhorst et al. (+1 more)
We consider the problem of approximate cloning of
quantum states: given $n$ copies of an unknown state $\rho \in \mathbb{C}^{d \times d}$, prepare an $(n+k)$-copy state with high fidelity to $\rho^{\otimes (n+k)}$. Werner's pure state cloner is the optimal channel for the pure state case, and shows that $n = \Theta(kd/\varepsilon)$ copies are necessary and sufficient to clone $k$ additional copies of an unknown pure state to fidelity $1-\varepsilon$. The random purification channel gives a straightforward extension of Werner's cloner to mixed state inputs: given $n$ copies of a mixed state, randomly purify your input, apply Werner's channel in the larger
Hilbert space, and then trace out the auxiliary registers. This gives a mixed state cloner using $n = O(krd/\varepsilon)$ copies to clone rank-$r$ states. Can one do any better? We show that the answer is no: one must use $n = \Omega(krd/\varepsilon)$ copies. We prove our lower bound by studying the special case of projector cloning, in which the input state $\rho$ is promised to be of the form $P/r$, where $P$ is a rank-$r$ orthogonal projector. As a further application of our techniques, we consider the closely related problem of approximate transposition of
quantum states, where one seeks to convert $\rho^{\otimes n}$ to a $k$-copy state with high fidelity to $(\rho^T)^{\otimes k}$. Here, we again show $n = \Theta(krd/\varepsilon)$ copies are necessary and sufficient for this task.
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All authors Marco Fanizza, Dmitry Grinko, Thilo Scharnhorst, Jack Spilecki
Quantum Physics
Efficient formation and identification of single emitters in 4H-SiC following maskless heavy ion implantation
S. Eserin, L. K. S. Zimmermann, E. Schneider et al. (+12 more)
Single
photon emitters in silicon carbide (SiC) are a leading platform for scalable
quantum technologies. Recent interest has focused on oxygen-vacancy-related emitters, which show exceptionally high optical brightness and strong
spin readout contrast. One barrier to scalable
quantum devices based on these emitters is the challenge of maskless formation and rapid identification. Here, we demonstrate the formation of isolated bright single emitters in 4H-SiC, using low-energy maskless implantation of heavy ions bismuth and tin. Following annealing, up to 18% of implanted sites host a single emitter, with optimal yields achieved at annealing temperatures of 900-1000 degrees C. Occupancy statistics are modelled to estimate the implantation dose that maximises single-emitter yield. We introduce a tiered characterisation scheme, where a simple intensity threshold isolates single-emitter candidates, confirmed through
photon correlation measurements, after which correlations between polarisation, saturation count rate and
magnetic resonance frequency assign emitter type. It is shown that time-consuming low-temperature spectroscopy is not necessary to distinguish emitter types. Together, maskless heavy-ion implantation and selective screening offer an efficient route to forming and rapidly identifying near-surface single emitters for room-temperature
quantum technologies such as
quantum sensing.
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All authors S. Eserin, L. K. S. Zimmermann, E. Schneider, M. Ludlow, J. Heiler, O. G. Lloyd-Willard, K. Stockbridge, G. Aresta, L. Antwis, S. K. Clowes, M. Hofmann, S. Kucera, P. Berwian, F. Kaiser, B. N. Murdin
Quantum Physics · Cross-listed from hep-lat
Efficient Quantum Simulations of Yang-Mills theory with Maximal-tree Gauge
Tianyin Li, Ying-Ying Li, Xiaoyang Wang et al. (+1 more)
We develop a
quantum algorithmic framework for the efficient simulation of Yang–Mills theories, including the $\mathrm{SU}(3)$ gauge theory in
Quantum Chromodynamics (QCD). The framework uses maximal-tree gauge in terms of gauge field variables that removes all local gauge redundancies. In the resulting gauge-fixed formulation and digitization in the field-amplitude basis, we show that
Hamiltonian time
evolution admits an efficient implementation based on
quantum singular value transformation (QSVT). We derive upper bounds on the total number of
qubits and gate complexity, finding
polynomial scaling with the inverse simulation precision $1/\varepsilon_s$,
lattice volume $\mathcal{V}$, gauge coupling $g$, and target energy scale $E$. Our results provide a rigorous complexity-theoretic demonstration that non-Abelian Yang–Mills theories can be simulated efficiently on
quantum computers, paving the way toward first-principles
quantum simulations of non-perturbative QCD dynamics.
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All authors Tianyin Li, Ying-Ying Li, Xiaoyang Wang, Hongxi Xing
Quantum Physics · Cross-listed from cond-mat.stat-mech
Long-time Dynamics of Many-body Open Quantum Systems using Quantum Generating Functions
Katha Ganguly, Dario Poletti and Bijay Kumar Agarwalla
The interplay between coherent
unitary evolution and environment-induced dissipation can give rise to a wide range of non-
equilibrium dynamics in open
quantum systems, ranging from interesting transport phenomena to dynamical phase transitions. However, accessing such long-time dynamics remains challenging for the existing methods developed for the simulation of many-body open
quantum systems. We address this problem by developing a
quantum generating function (QGF) formalism for open many-body systems for both ensemble-averaged dynamics governed by a Markovian
quantum master equation and trajectory-resolved dynamics described by the
quantum trajectory formalism, including
quantum jumps, and
quantum state
diffusion. Our approach computes the dynamics of higher-order moments and fluctuation statistics without explicitly evolving the
quantum state, thereby providing an efficient and scalable approach for investigating many-body open
quantum systems. We demonstrate the versatility of the formalism by applying it to both the integrable open XXZ chain and the nonintegrable open next-nearest-neighbor XXZ
spin chain, where it uncovers distinct initial state dependent long-time transport regimes. Our work establishes
quantum generating functions as an efficient and scalable framework for investigating long-time dynamics in open
quantum many-body systems.
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Quantum Physics
Tight Bounds for Purity and Product Testing from Partial Transposition
Oren Akresh and Jacob Beckey
Coherent measurements across multiple copies of an unknown
quantum state can substantially reduce the number of samples required to learn its properties, but remain experimentally challenging. Current experiments typically prepare and measure one copy at a time, potentially adapting later measurements to earlier outcomes. A central challenge is adaptivity, which makes the space of possible measurement strategies difficult to characterize. The positive-partial-transpose (PPT) relaxation bypasses this complexity by considering a larger, mathematically tractable class of measurements, at the risk of weakening the resulting bounds. Here we show, surprisingly, that the relaxation loses nothing at the level of asymptotic sample complexity for two fundamental tasks: purity testing and product testing. In both cases, lower bounds against the full class of PPT measurements are matched by nonadaptive single-copy protocols. Moreover, our proof requires only basic symmetric subspace identities, providing a simple route to sharp lower bounds for adaptive single-copy measurements.
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Quantum Physics · Cross-listed from math.NA
QH-GEM: Quantum-Hydrodynamic Generative Modeling
Harbir Antil, Alex Kaltenbach and Sarswati Shah
In this paper, we develop a deterministic, physically constrained generative framework based on the Madelung formulation of the free-particle Schrödinger equation. A reference Born probability density and a controllable initial phase function serve as initial data for the free Madelung system, which couples the Born probability density and phase function through the Bohm
quantum potential, while the phase function determines the hydrodynamic velocity field. Provided that the Born probability density remains positive and the hydrodynamic velocity field generates a unique global characteristic flow, samples drawn from the reference density and transported along the characteristic flow are distributed according to the evolving Born probability density at every time. As a consequence, randomness enters only through the initial sampling; the subsequent generation is deterministic and involves neither
stochastic dynamics nor an independently parameterized time-dependent velocity field. We formulate terminal-time distribution matching as a PDE-constrained phase-identification problem and derive the underlying
Hamiltonian and Fisher-information structure. For isotropic Gaussian wave packets, we obtain explicit dynamics and a necessary and sufficient condition for exact reachability of isotropic Gaussian targets by quadratic initial phase functions, together with the corresponding sampling map. For a smooth prescribed potential initial velocity field, we further establish that the characteristic flow approximates the associated first-order transport map with an O(T^2) error, both uniformly and in the 1- and 2-Wasserstein distances. A numerical Gaussian
benchmark validates the fully discrete forward solver, while full-grid PDE-constrained phase identification is demonstrated for asymmetric bimodal targets.
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Quantum Physics
The Find Rows and Columns and Decode algorithm for quantum expander codes
Dimiter Ostrev
A new adaptation of the Find Erasures and Decode
algorithm from classical to
quantum expander codes is presented. It runs in linear time and is parallelizable to logarithmic depth. Compared to Small Set Flip and Small Set Find, the new
algorithm avoids the overhead of considering the subsets of stabilizer generators, requires less expansion and corrects more errors.
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Quantum Physics
Strong Converse Exponent of Quantum State Merging
Mario Berta, Hao-Chung Cheng, Roberto Rubboli et al. (+1 more)
We determine the strong converse exponent for the
entanglement cost of
quantum state merging, showing that it is characterized by the optimized $\alpha$-$z$ conditional Rényi
entropies with $z=\alpha/2\in[1/2,1]$. This contrasts with the sandwiched conditional Rényi
entropies that typically govern strong converse exponents in
quantum information theory. As a consequence, we derive the strong converse exponent of the partially smoothed conditional min-
entropy in purified distance. This exponent is governed by club-sandwiched conditional
entropies, whereas global smoothing leads to a sandwiched expression.
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All authors Mario Berta, Hao-Chung Cheng, Roberto Rubboli, Marco Tomamichel
Quantum Physics
Conditional contraction coefficients and their applications to quantum networks
Christoph Hirche, Ian George, Theshani Nuradha et al. (+1 more)
Contraction coefficients quantify the loss of distinguishability induced by a channel and provide a strong form of the data-processing inequality. While standard contraction coefficients ignore auxiliary
quantum systems, existing extensions based on complete contraction coefficients require the compared states to have identical reference marginals. In this work, we introduce conditional contraction coefficients, a novel family that incorporates arbitrary
quantum reference systems by subtracting the distinguishability already present in the reference system. We develop a general framework for contraction coefficients with such
quantum side information, including the corresponding strong-data-processing-inequality (SDPI) constants, expansion coefficients, and relative contraction coefficients. For the trace distance, we show that the optimization can be restricted to orthogonal input states. For the
quantum relative
entropy, we prove that its conditional contraction coefficient is exactly equal to the contraction coefficient of the conditional mutual information, extending the classical correspondence between relative-
entropy contraction and mutual-information contraction to the setting with
quantum side information. More generally, we identify structural properties of divergences required for these results and discuss extensions beyond the relative
entropy. These results establish a unified framework for analyzing information contraction in
quantum network settings, where
quantum side information and distributed correlations are intrinsic features of the information-processing task. Applications include an extension of the Polyanskiy-Wu bounds on mutual information contraction, new perspectives on mixing times, and fundamental limits on
quantum memories.
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All authors Christoph Hirche, Ian George, Theshani Nuradha, Mark M. Wilde
Quantum Physics
Dynamics and spectra of open quantum systems coupled to anharmonic environments
Kian Damezin, Brendon W. Lovett, Erik M. Gauger et al. (+1 more)
In open
quantum systems, the environment is typically modelled as a collection of harmonic oscillators, whereas realistic environments often exhibit unique non-Markovian effects due to the anharmonicity of the environment. Here we present a framework for modelling anharmonic environments in open
quantum systems numerically exactly, in which, via a matching criterion, we map the anharmonic environment onto an effective harmonic one. This results in an effective spectral density that is a collection of shifted bare spectra arising from the non-equidistant energy gaps of the anharmonic environment, along with a unique zero-frequency term that effectively acts as static disorder on the system. This is due to the non-zero variance of the diagonal of the bath coupling operator. In tandem, we develop a framework for investigating the effects of environments comprising a few damped anharmonic modes where the matching criterion fails to work due to the non-Gaussianity of the environment. For both continuous and discrete damped anharmonic environments, this work investigates their unique influence on the system's dynamics, including enhanced non-Markovianity compared to a harmonic approximation, novel effects in the absorption spectrum, and the potential for anharmonic environments to enhance energy transport.
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All authors Kian Damezin, Brendon W. Lovett, Erik M. Gauger, Adam Burgess
Quantum Physics
Optimal Gaussian networks for private distributed quantum sensing
Hanbom Yoo, Byeongyun Yang, Hyunwoo Yoo et al. (+1 more)
Private distributed
quantum sensing aims to estimate an authorized collective parameter while preventing independent estimation of individual local parameters. Here, we analytically characterize Gaussian
quantum networks satisfying this perfect local
privacy condition. Using a graph representation of the Gaussian pairing
matrix, we show that two-mode squeezed
vacuum states constitute the essential building blocks of
privacy-preserving Gaussian states. We then analytically derive the optimal sensitivity under perfect local
privacy and determine a Gaussian probe that achieves Heisenberg scaling with respect to both the
photon number and the number of sensing modes. Using local homodyne measurements and maximum-likelihood estimation, we numerically verify
quantum-enhanced sensitivity beyond the shot-noise limit while preserving perfect local
privacy. We further show that the local-
privacy condition is preserved under arbitrary phase-independent
quantum channels, including optical loss. Our results provide a general framework for constructing and optimizing
privacy-preserving continuous-variable
quantum sensing networks.
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All authors Hanbom Yoo, Byeongyun Yang, Hyunwoo Yoo, Seongjin Hong
Quantum Physics
Programmable Cavity Squeezing for Distributed Sensing in a Tweezer Array
Youssef Trifa, Marco Fattori and Luca Pezzè
Field sensing with state-of-the-art atom interferometers is restricted to the use of uncorrelated devices op- erating in parallel. We can overcome this limitation by using distributed sensing protocols where
quantum correlations among spatially-separated devices are engineered in the spatial mode carrying the signal. We show that a tweezer array in a cavity offers an ideal testbed to engineer
quantum states for distributed sensing, with the possibility to generate
entanglement both within and between the clouds. The competition between local and intercloud cavity-mediated exchange allows the sign and spatial pattern of the intercloud couplings to select the squeezed mode. For two ensembles, positive coupling produces uniform collective squeezing, whereas negative coupling generates strong staggered, nonlocal squeezing. A semiclassical analysis reveals a counter-twisting- like phase-space flow, qualitatively distinct from standard one-axis twisting. The analysis and results can be further generalized to a larger number of ensembles. We apply the scheme to differential Ramsey interferometry with common phase noise spanning the full 2 \pi range, the resulting staggered states reduce the phase uncertainty below the standard
quantum limit, with an ellipse
estimator approaching the Cramèr-Rao bound. These results establish programmable cavity interactions as a scalable route to
entanglement tailored to distributed signals.
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Quantum Physics
Kramers pseudospin and the quantum number proposed for the many-electron Dirac?Coulomb Hamiltonian
Shadan Ghassemi Tabrizi
The square of a sum of single-electron time reversals has been proposed as a conserved quantity with an integer
eigenvalue spectrum for the many-electron Dirac-Coulomb
Hamiltonian [Phys. Rev. A 94, 052104 (2016)], and its expectation value is in use as a diagnostic of Kramers contamination. This work identifies the operator behind the construction, a component of a pseudospin attached to the chosen Kramers pairs, whose angular-momentum
algebra reproduces the reported spectrum and yields the eigenvectors in closed form. The label $k$ entering the proposed
quantum number $-k^2$ is twice the magnitude of a pseudospin projection onto an axis fixed by the basis and changes when the Kramers pairs are rephased. The commutation with the
Hamiltonian is unfounded, and the proposed
quantum number does not stand.
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Quantum Physics
Towards Reproducible Evaluation of Distributed Quantum Circuit Partitioning Algorithms
Javier Vela-Tambo, Davud Azizov and Tian Guo
Distributed
Quantum Computing (DQC) addresses the physical scaling limitations of monolithic
quantum processors by networking modular
Quantum Processing Units (QPUs). Efficient execution of
quantum algorithms on DQC architectures requires compiling them across QPUs while minimizing inter-QPU communication bottlenecks, primarily through
circuit partitioning. However, current evaluations of state-of-the-art partitioning heuristics focus primarily on the total
entanglement cost of the partitions, failing to capture the broader structural and temporal overheads introduced by distributed network constraints. This paper addresses this evaluation gap by applying established monolithic benchmarking metrics to partitioned distributed
circuits to quantify the performance impact of network constraints. Using an open-source, automated evaluation pipeline, we systematically assess diverse partitioning
algorithms across standardized workloads and
quantum network
topologies. Our empirical results reveal that partitioning
algorithms with comparable
entanglement costs can still introduce drastically different physical execution penalties. By exposing these hidden trade-offs, such as severe increases in
circuit depth and substantial reductions in gate density, this study demonstrates that comprehensive
circuit-level metrics are essential for guiding the future design of DQC compilers.
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Quantum Physics
Fast On-Chip Thermometry with TiN Kinetic Inductance Resonators in 22 nm Process Technology
Johann Drayne, George Ridgard, Lorenzo Peri et al. (+9 more)
Understanding the temporal and spatial dependence of temperature is critical in high-performance cryogenic devices. Typical thermometry techniques struggle to simultaneously combine high bandwidth, sensitivity and on-chip integration, limiting their ability to measure fast intra-device thermal fluctuations. Here, we demonstrate a time-resolved thermometry platform based on TiN kinetic inductance resonators integrated in a 22 nm FDSOI chip. By tracking temperature-dependent shifts in the resonant frequency, we achieve sub-millikelvin temperature sensitivity down to temperatures of 100 mK. Time-resolved on-chip pulsed heating experiments as a function of distance reveal an onset delay, consistent with a quasi-ballistic heat propagation velocity of 3.9 ${\pm}$ 0.1 mm ${\mu}$s${}^{-1}$. We also show that elevated temperatures increase net thermal conductance, shortening thermal relaxation times across all spatial separations. This behaviour manifests in two distinct regimes: a substrate-limited regime at 100 mK, where cooling rates vary with heater distance, and a Kapitza boundary-limited regime at 400 mK, where thermal relaxation becomes more spatially uniform. These measurements demonstrate kinetic inductance thermometry's ability to rapidly probe non-
equilibrium temperature dynamics in cryogenic devices such as
quantum processors.
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All authors Johann Drayne, George Ridgard, Lorenzo Peri, Frederic Schlattner, Fabio Olivieri, Mathieu de Kruijf, Isaac Harris, Grayson Noah, James Kirkman, Alberto Gomez-Saiz, M. Fernando Gonzalez-Zalba, Thomas Swift
Quantum Physics
A Superconducting Phase Transition Single-Electron Transistor
Gorka Aizpurua-Iraola, Thomas H. Swift, Felix-Ekkehard von Horstig et al. (+6 more)
Quantum computers require fast and accurate methods for
qubit state detection. Phase-transition sensors exploit the abrupt change between two physical states of a material to achieve enhanced sensitivity and have enabled advanced detectors for
quantum technologies, such as superconducting nanowire single-
photon detectors. However, this sensing principle has not yet been applied to
semiconductor spin qubits. Here, we demonstrate a superconducting phase-transition
radio-frequency single-electron transistor (PTSET), a charge sensor for
semiconductor spin qubits whose response is enhanced by a superconducting-to-normal phase transition. The transition is engineered by linking the sensor current to a low-critical-current, high-kinetic-inductance inductor integrated into the
radio-frequency matching network. We demonstrate improvements in sensitivity of one and two orders of magnitude over conventional rfSETs in the large- and small-signal regimes, respectively. Our results establish phase-transition sensing as a route towards ultrasensitive, integrated charge sensors for
semiconductor quantum computing and point to broader applications, including cryogenic
photon detection for
radio astronomy.
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All authors Gorka Aizpurua-Iraola, Thomas H. Swift, Felix-Ekkehard von Horstig, Domenic Prete, James Kirkman, Grayson M. Noah, Fabio Olivieri, Alberto Gomez-Saiz, M. Fernando Gonzalez-Zalba
Quantum Physics · Cross-listed from cond-mat.quant-gas
Crossing the Rotational Sound Barrier in a Quantum Solvent
Baptiste Coquinot, Giacomo Bighin, Mikhail Lemeshko et al. (+1 more)
Molecules embedded in superfluids provide an experimentally controllable platform for investigating
impurity physics. Here, we investigate a driven molecule rotating in a superfluid environment, including helium and Bose–Einstein condensates, at rotation frequencies similar to the bath dynamics. Within the experimentally relevant platform of an optical centrifuge, we show that the rotor remains localized up to a characteristic harmonic frequency that can realistically exceed the excitation energies of the bath, enabling access to ultrafast rotating
impurities. In the co-rotating frame, the bath excitations experience a rotational Doppler shift, generating angular-momentum-resolved resonances absent in
equilibrium angulon theory. We identify a dissipative rotational sound barrier at which the molecule resonantly emits bath excitations and undergoes strong angular momentum exchange with the surrounding medium. Overall, we establish the dynamical phase diagram of the driven rotor in a
quantum solvent and introduce a generic platform for investigating fast driven rotating
impurities in
quantum many-body systems.
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All authors Baptiste Coquinot, Giacomo Bighin, Mikhail Lemeshko, Ragheed Alhyder
Quantum Physics · Cross-listed from math.NA
A quantum-assisted framework for PDE-based Bayesian inverse problems
Dong An, Yinan Li, Pucheng Tang et al. (+1 more)
Quantum computing offers potential advantages for solving partial differential equations (PDEs). However, most existing
quantum PDE solvers primarily focus on preparing
quantum states for solutions, while the efficient recovery of classical information from these states remains less explored. Motivated by the readout limitation, we propose a
quantum-classical hybrid framework for
Bayesian PDE inversion problems: The
quantum processor evolves the PDE and evaluate the loss function with sampling noises, while the classical computer tunes the hyper-parameters in the Gaussian Process Regression to explore the next trial candidate. To match the
quantum solvers for linear and semi-linear autonomous
evolution PDEs, we suggest to use a normalized
quantum-state loss as the data-misfit function and evaluate the new misfit by combining
quantum PDE solvers with the Hadamard test, thereby allowing us to extract useful classical information using only a limited number of
quantum state copies without reconstructing the full solution vector. The analysis of error propagation and overall complexity of loss evaluation under a prescribed accuracy shows that the new data-misfit function outperforms the conventional L2-loss under
quantum measurements.
Quantum circuit simulations of 1D and 2D linear convection
diffusion equations under approximate and finite sampling loss evaluations, together with classical numerical experiments on a nonlinear forced viscous Burgers equation, demonstrate the feasibility of the proposed approach for parameter inversion even when the loss evaluations are affected by sampling noise. This framework may provide a viable
quantum-assisted scheme for PDE-based inverse problems and elucidate the potential of
quantum PDE
algorithms in addressing a complete
quantum-to-end optimization stack.
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All authors Dong An, Yinan Li, Pucheng Tang, Yunfeng Xiong
Quantum Physics · Cross-listed from physics.flu-dyn
Quantum-Inspired Computational Fluid Dynamics for Transient Turbulent Compressible Flows
Shang Xian Matthew Lee, Melissa Kozul, Muhammad Usman et al. (+3 more)
Quantum-inspired
algorithms are an emerging class of
algorithms for computational fluid dynamics (CFD) with potentially favourable scaling for large problems compared to classical methods. However, their applications have been limited to incompressible flows due to arithmetic limitations, which are addressed in this work. This work introduces the first true end-to-end
quantum-inspired computational fluid dynamics (QICFD) solver for direct numerical simulation of the compressible Navier-Stokes equations, that is, all arithmetic operations, as well as initialisation and post-processing, are undertaken in the tensor train (TT) format. Importantly, new division and square-root
algorithms using TTs enable the use of Sutherland's law for viscosity, and leverages recent improvements in TT arithmetic
algorithms for reduced runtime and
memory cost. The new QICFD solver is validated by comparison with the classical CFD solver HiPSTAR and by way of a challenging fluid-flow test case, the low resolution Taylor-Green
Vortex (TGV) at Mach numbers of 0.8 and 0.1. The TGV test case is a transient turbulent case that is very sensitive to accumulating errors, yet our QICFD solver achieves excellent agreement with the classical CFD reference. This work demonstrates the correctness of the new TT division and square-root
algorithms, and that QICFD is capable of compressible flow simulations. The new QICFD solver is also able to perform simultaneous simulations, running multiple TGV-like cases initialised differently in parallel with reduced extra cost. Finally, the demonstrated TGV test case reveals additional challenges of QICFD as well as highlight the need for future advances to make TT methods viable for industrially-relevant conditions.
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All authors Shang Xian Matthew Lee, Melissa Kozul, Muhammad Usman, Martin Sevior, Matthew L. Sims-Goh, Richard D. Sandberg
Quantum Physics
Quantum-enhanced ghost imaging recognition via joint optimization of speckle patterns and quantum network parameters
Yirui Mao, Xiangyu Ge, Yuhang Tu et al. (+3 more)
Ghost imaging enables nonlocal image reconstruction and exhibits strong robustness against interference, but achieving high-fidelity recognition at ultra-low sampling rates remains challenging.
Quantum machine learning offers a novel approach for efficient feature extraction on noisy medium-scale
quantum devices; however, existing methods generally suffer from low recognition accuracy and weak noise resistance. This paper proposes a ghost imaging recognition method based on the simultaneous optimization of speckle patterns and
quantum network parameters. By leveraging the mathematical equivalence between classical convolution and speckle-object dot product operations in ghost imaging, a speckle consistency regularization mechanism is introduced to achieve end-to-end joint optimization of optical coding and
quantum feature extractors. A parallel 8-
qubit quantum circuit employing block coding and a
star-shaped
entanglement structure is designed to extract higher-order features from bucket signals. Simulation results on the MNIST and Fashion-MNIST
datasets show that at an ultra-low sampling rate of 1.5625%, the proposed framework achieves recognition accuracies of 90.1% and 81.7%, respectively, representing a 2.6% improvement over classical convolutional neural networks and a maximum improvement of 14.2% over traditional hybrid
quantum machine learning models. This method also exhibits strong robustness to
quantum noise and has been validated on a real optical ghost imaging system, achieving an average recognition accuracy of 84.8%. These results confirm that the joint optimization of speckle patterns and
quantum network parameters provides a reliable and practical solution for low-sampling ghost imaging recognition.
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All authors Yirui Mao, Xiangyu Ge, Yuhang Tu, Anqi Zhang, Le Wang, Shengmei Zhao
Quantum Physics
Isotropic Nanoscale Quantum Sensor at Room-Temperature
Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste et al. (+9 more)
Color-center based
quantum sensors provide nanoscale resolution under ambient conditions, yet their applicability remains limited. Because the quantization axes are locked to the host
lattice, conventional color centers suffer severe signal loss in off-axis
magnetic fields. To address this, we report an isotropic magnetometer enabled by the neutrally charged nitrogen-vacancy center (NV0) in diamond. Here,
spin-to-charge dynamics yield an NV0-dark
spin pair whose quantization axis dynamically aligns with the external field. Read out through NV charge-state-selective fluorescence, this system exhibits microsecond room-temperature coherence and nanotesla sensitivity for arbitrary field directions. We demonstrate
alignment-free mapping of steep field gradients and single paramagnetic micro-targets, alongside isotropic readout from randomly oriented nanodiamonds. Resolving longstanding orientation constraints, this platform unlocks unrestricted nanoscale magnetometry across life sciences and
quantum materials.
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All authors Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste, Dhruv Wadhwani, Olt Gashi, Daniel A. García Vaca, Mokessh K. Ciwan, Simone P. Crozier, Christian Laube, Sirswa K. Shree Ram, Matteo Slaviero, Nabeel Aslam
Quantum Physics
Cavity-assisted homodyne detection with a single photodiode
Jonas Junker
High-frequency squeezed states are important for
quantum metrology and information processing, but quadrature measurements at gigahertz frequencies remain challenging. Balanced homodyne detection (BHD), the standard approach, requires closely matched complex transfer functions in both photodetection channels to suppress local-oscillator (LO) noise and maintain a well-defined readout quadrature. This matching becomes increasingly difficult at high bandwidths. Strongly asymmetric single-photodiode homodyne detection avoids this requirement, but achieving high signal efficiency and shot-noise clearance typically requires hundreds of milliwatts of LO power and does not suppress technical LO sidebands. I propose cavity-assisted homodyne detection, in which the
quantum field and LO enter separate ports of an impedance-matched traveling-wave cavity. The resonant LO carrier is transmitted to the photodetector, where it beats with off-resonant signal sidebands reflected from the cavity. At the same time, technical LO sidebands outside the cavity linewidth are suppressed. I derive the
quantum input-output relations and linearized photocurrent including intracavity loss, and show that near-unity signal-transfer efficiency can be achieved at moderate incident LO power. The cavity linewidth and free spectral range determine the usable detection band.
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Quantum Physics
Corrections induced by the GUP to the Lamb shift of an accelerated atom interacting with a quantum scalar field
Zhi Wang, Yi Yang and Zhengwen Long
We investigate the effect of the GUP on the Lamb shift of a two-level atom interacting with a real massless scalar
quantum field, within the DDC formalism. For an atom undergoing inertial motion, uniform acceleration, and uniform circular motion, we analyze the separate contributions of
vacuum fluctuations and radiation reaction. We first derive the statistical functions of the field along the atom's trajectories for the three types of motion, expressing them as frequency integrals, and then employ them to calculate the
vacuum fluctuation and radiation reaction contributions to the radiative level shift. We show that the GUP-modified Lamb shift of the two-level atom arises entirely from
vacuum fluctuations and acquires additional corrections proportional to $\beta$. We focus in particular on the acceleration-dependent GUP corrections. For a uniformly accelerated atom, the GUP corrections comprise thermal and nonthermal parts. At low accelerations, the thermal part exhibits nonmonotonic behavior, and is proportional to $a^4$ in the limit $a/\omega_0 \to 0$; the nonthermal part, by contrast, grows nonlinearly and monotonically, exceeding the thermal part by nearly two orders of magnitude at large accelerations. For an atom in uniform circular motion, the GUP corrections are purely nonthermal and also display a nonlinear, monotonic dependence on acceleration, increasing or decreasing steeply according to the sign of $\beta$. For the same $\beta$, the corrections are larger in uniform circular motion than in uniformly accelerated motion, since the former involves terms proportional to both $a^2$ and $a^3$, whereas the latter contains only $a^2$ terms.
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Quantum Physics
Davide Rinaldi, Mattia Moroder, Dario Gerace et al. (+2 more)
Fast and reliable
qubit reset is essential for the efficient operation of
quantum processors. Among the proposed strategies, Mpemba-effect-based protocols offer a simple route to accelerated relaxation, but provide limited insight into the optimality of the full reset dynamics.
Geometric approaches, by contrast, quantify optimality but do not generally suggest practical acceleration protocols. Here, we bridge these perspectives through a
geometric analysis of
entanglement-assisted
qubit reset. We show that entangling operations can redistribute local coherences across a multi-
qubit register, allowing the reduced state of each
qubit to follow a geodesic path towards the ground state. Remarkably, this locally optimal behaviour can emerge even when the collective
evolution becomes suboptimal in the full state space. We illustrate this interplay for different families of initial multi-
qubit states. Our results provide a
geometric perspective on Mpemba-inspired reset acceleration and clarify when extending two-
qubit protocols to larger registers provides a further advantage in the reset process.
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All authors Davide Rinaldi, Mattia Moroder, Dario Gerace, Giacomo Guarnieri, Steve Campbell
Quantum Physics
Correcting Connectivity in Arc-Based QUBO Models for Fixed-Fleet Vehicle Routing
Omer Gurevich, Maor Matityahu, Tal Mor et al. (+1 more)
We revisit a degree-only arc
Hamiltonian for fixed-fleet, homogeneous, uncapacitated vehicle routing. Its local penalties define only a cycle cover, so ground states may contain customer cycles disconnected from the depot. We construct a
polynomial-size quadratic unconstrained binary optimization (QUBO) repair using capped single-commodity flow and prove connected, cost-optimal ground-state routings under explicit penalty assumptions. For $N-1$ customers and $K$ nonempty routes, the unreduced encoding uses exactly $|E|(1+\lceil\log_2(N-K+1)\rceil)$ logical problem
qubits. A reversible compute-phase-uncompute implementation evaluates the flow penalties in $O(N^2\log N+N\log^2N)$ logical gates on a complete graph, using $O(\log N)$ reusable workspace and no product register. On complete loopless graphs, a position encoding that arranges all routes in one sequence separated by depot occurrences uses fewer problem
qubits and written terms when the number of bits per flow register grows. Under the same reversible accounting model, the flow formulation admits a smaller logical-gate upper bound. Exact
Hamiltonian and
circuit audits and a
benchmark of 1,200 cost
matrices verify the formulation and quantify the connectivity gap. A 32,000-shot Amazon Braket task on IQM Emerald characterizes depth-one termwise Ising
circuits for a diagnostic $N=4$, $K=1$ counterexample. In the degree-only
circuit, 78.05% of selected $p=1$ shots realize the invalid disconnected ground state; the reduced 14-
qubit flow-augmented
circuit yields no fully feasible sample. These device results characterize mapped
Hamiltonians and compilation, not an asymptotic advantage in solving routing problems.
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All authors Omer Gurevich, Maor Matityahu, Tal Mor, Aryeh Lev Zabokritskiy
Quantum Physics
Quantum Interconnects Part I: Strategic Quantum Network Formation
Gustavo Castro do Amaral
The realization of large-scale
quantum networks requires more than advances in
quantum repeaters,
memories, and processors, it requires a framework explaining how heterogeneous
quantum technologies evolve from isolated deployments into interconnected infrastructures. While the classical Internet evolved under strong utility incentives associated with resource sharing and communication demands,
quantum networking currently lacks dominant applications capable of generating comparable incentives. As a consequence, contemporary
quantum networks are largely formed through technology-driven decisions motivated by technical feasibility, experimental validation, and expected future value. This work argues that the absence of utility-driven network formation is not solely a consequence of immature applications, but also of insufficient abstraction. In particular, heterogeneous
quantum platforms remain tightly coupled to the functionalities they provide, preventing the definition of technology-independent utility functions. A hierarchical architecture consisting of Physical Platforms (PP), Functionalities (F), Services (S), Applications (A), and Use-Cases (UC) is proposed, together with the argument that
quantum interconnects constitute the enabling technology required to decouple physical implementations from network functionalities. Such decoupling permits the definition of utility functions at the functionality level and establishes the conditions under which strategic (
agent-based) network formation becomes applicable.
Quantum interconnects should therefore be viewed not only as interoperability devices, but also as fundamental enablers of strategic
quantum network
evolution.
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Quantum Physics · Cross-listed from nucl-th
Coupled-channel scattering from artificial confinement
Tafat Weiss Attia, Itay Horin and Betzalel Bazak
Artificial confinement encodes continuum scattering information in discrete, bound-state-like spectra, allowing reaction observables to be extracted with finite-basis or finite-domain methods. We apply this strategy to a two-channel cluster model of $^4$He with open $^3$H+p and $^3$He+n channels. We extract coupled-channel observables from spectra generated by a harmonic-oscillator (HO) trap, a spherical hard wall, and, within a single-partial-wave truncation, a periodic cubic box. The three geometries are formulated in a unified quantization-condition framework and benchmarked against a continuum $R$-
matrix calculation. Above the second-channel threshold, several confined levels at a common scattering energy are combined in an overdetermined fit to determine two phase shifts and an inelasticity. Without Coulomb interactions, all three geometries yield consistent results for the $^1S_0$ and $^3P_1$ partial waves. With Coulomb interactions in the charged $^3$H+p channel, the HO and spherical-wall results also agree closely with the continuum reference. A Monte Carlo propagation study shows that spectral uncertainties are amplified near trap-function poles and along poorly conditioned directions associated with the inelasticity and phase-shift difference, whereas the phase-shift sum remains comparatively robust. These results provide a controlled
benchmark for confinement-based scattering methods and delineate their strengths and limitations for future few-body and ab initio reaction calculations.
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Quantum Physics
Bound-state-mediated remote charging of a quantum battery
Jian-Jian Cheng, Hai-Bo Qiu, Lin Zhang et al. (+1 more)
Remote charging of a
quantum battery (QB) is hindered by radiative leakage of the excitation into the photonic environment that acts as a mediator for energy transfer. We consider a charger-battery model consisting of two two-level systems (TLSs) that are locally coupled to two sites of a one-dimensional coupled cavity array. When their transition frequency lies outside the propagation band, the system forms atom-
photon bound states with localized photonic components, and the overlap of these components lifts the degeneracy of the even- and odd-parity bound states, yielding an energy splitting that drives coherent energy transfer from the charger to the QB. In this way, the band gap suppresses resonant emission and the localized bound states mediate remote charging. From the parity-resolved spectrum, we relate the charging time to the energy splitting and the charged ergotropy to the fraction of TLS population on the bound states. Bound states closer to the band edge extend the interaction range of the TLSs but contain a large photonic fraction and are consequently more susceptible to
photon loss.
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All authors Jian-Jian Cheng, Hai-Bo Qiu, Lin Zhang, Ming-Liang Hu
Quantum Physics
Energy Ordering from Nonlinear Quantum Dissipation
Alireza Ataei, Olle Eriksson and Vahid Azimi-Mousolou
Energy-ordered occupation is deeply embedded in
quantum physics, from the Aufbau principle governing the filling of electronic states in atoms and molecules to the emergence of low-energy configurations in
quantum many-body systems. However, the dynamical mechanism by which a generic
quantum state develops such an energy hierarchy remains a fundamental question. Here we show that such an energy hierarchy can emerge dynamically from nonlinear
quantum dissipation. Rather than being imposed as a principle or generated through coupling to a thermal reservoir, an Aufbau-like ordering of energy levels emerges intrinsically under
quantum Landau-Lifshitz-Gilbert dynamics from a generic initial mixed state. This convergence is a nontrivial consequence of Lyapunov monotonicity and instability of disordered population configurations. The resulting dynamics establish an intrinsic nonlinear mechanism for organizing density-
matrix populations and provides a route toward selective preparation of low-energy subspaces. Numerical simulations confirm analytical predictions and illustrate convergence toward low-energy sectors.
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Quantum Physics
Quantum Rare-Event Estimation for Ising Graphical Models with Belief-Propagation State Preparation
Mario Hernández Vera, Narges Jamialahmadi, Burak Mete et al. (+2 more)
Quantum amplitude estimation can reduce the sampling cost of rare-event probability estimation, but applying it to correlated Ising graphical models is limited by the difficulty of preparing the target distribution and building a practical event oracle. This work explores two approximate strategies for mitigating these challenges. We introduce a sample-free state-preparation method combining loopy belief propagation with the Chow–Liu
algorithm. The resulting tree approximation is compiled into a
quantum circuit with linear gate count and depth, and its accuracy is evaluated across graph families spanning different
topologies, coupling strengths, and coupling signs. We also construct a structural oracle that evaluates threshold rules with reversible Boolean gates. Using a twenty-node supply-chain disruption model as a case study, we compare maximum likelihood amplitude estimation against four classical Monte Carlo baselines. Under the fixed-depth schedule used throughout this work, the
quantum estimator has the same asymptotic error scaling as the classical methods but achieves lower estimation error by a constant factor. This reduction narrows when amplitude-encoding queries replace raw shots as the resource metric. We separate statistical error from the deterministic errors caused by approximate state preparation and oracle construction, and identify the requirements for achieving an improvement beyond a constant factor.
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All authors Mario Hernández Vera, Narges Jamialahmadi, Burak Mete, Susanne Schneider, Marco De Pascale