Quantum Physics
Chaos, Entanglement and Measurement: Field-Theoretic Perspectives on Quantum Information Dynamics
Anastasiia Tiutiakina
This work develops tools to understand how
quantum information spreads, scrambles, and is reshaped by measurements in many-body systems. First, I study scrambling and pseudorandomness in the Brownian Sachdev-Ye-Kitaev (SYK) model, quantifying pseudorandomness using
unitary k-designs and frame potentials. Using Keldysh path integrals with replicas and disorder averaging, I obtain analytic control of the approach to randomness, identify collective modes that delay convergence to Haar-like behavior, and estimate design times as functions of model parameters, clarifying links between scrambling, complexity growth, and random-
circuit phenomenology. Second, I construct a field theory for weakly measured SYK clusters. Starting from a system-ancilla description and a continuum monitoring limit, and using fermionic coherent states with replicas and disorder averaging, I derive a nonlinear sigma model that captures measurement back-action and the competition between interaction-induced scrambling and information extraction, predicting characteristic crossover scales and response signatures that distinguish weak monitoring from fully
unitary evolution. Third, I develop a strong-disorder renormalization group for measurement-only SYK clusters, based on the SO(2n) replica
algebra and Dasgupta-Ma decimation rules. The flow shows features reminiscent of infinite-randomness behavior, but an order-of-limits subtlety renders the leading recursions non-robust, so the analytic evidence for an infinite-randomness fixed point is inconclusive, even though the average second Renyi
entropy displays logarithmic scaling. Together, these results provide a unified
language to diagnose when many-body dynamics generate operational randomness and how measurements redirect that flow.
Read the full abstract ▾
Quantum Physics
On Simplest Kochen-Specker Sets
Mladen Pavicic
In Phys. Rev. Lett. 135, 190203 (2025) a discovery of the simplest 3D contextual set with 33 vertices, 50 bases, and 14 complete bases is claimed. In this paper, we show that it was previously generated in
Quantum 7, 953 (2023) and analyze the meaning, origin, and significance of the simplest contextual sets in any dimension. In particular, we prove that there is no ground to consider the aforementioned set as fundamental since there are many 3D contextual sets with a smaller number of complete bases. We also show that automatic generation of contextual sets from basic vector components automatically yields all known minimal contextual sets of any kind in any dimension and therefore also the aforementioned set in no CPU-time. In the end, we discuss varieties of contextual sets, in particular Kochen-Specker (KS), extended KS, and non-KS sets as well as ambiguities in their definitions.
Read the full abstract ▾
Quantum Physics
Optimal Distributed Similarity Estimation of Quantum Channels
Congcong Zheng, Kun Wang, Xutao Yu et al. (+2 more)
We study the query complexity of estimating the similarity of two unknown
quantum channels available at separated devices. For channels $\mathcal{E}$ and $\mathcal{F}$ on a $d$-dimensional system, the target functional is the normalized Choi overlap ${\rm Tr}[J_{\mathcal{E}} J_{\mathcal{F}}]/d^2$, where $J_{\mathcal{E}}$ and $J_{\mathcal{F}}$ are unnormalized Choi operators. We call this task distributed similarity estimation of
quantum channels (DSEC). Our main result is a tight characterization: estimating this overlap to additive error $\varepsilon$ with constant success probability requires and is achievable with \begin{align*} \Theta\!\left(\max\left\{\frac{\sqrt d}{\varepsilon},\frac{1}{\varepsilon^2}\right\}\right) \end{align*} queries to each channel. The lower bound holds even for the most general model considered here, allowing arbitrary ancillas, coherent adaptive access,
quantum memory within each laboratory, and multi-round classical communication. The dimension-dependent term follows from a shared-versus-independent Haar-
unitary testing problem, while the $\varepsilon$-dependence is obtained through a random-phase channel construction. Conversely, we give a non-adaptive, ancilla-free, incoherent randomized-measurement protocol for arbitrary channels that attains the same scaling. The protocol uses only shared classical randomness to coordinate local state preparations and measurement bases. For
unitary channels, our protocol reduces the dimension-dependent upper bound from $d/\varepsilon$ for independent coherent shadows to $\sqrt d/\varepsilon$. These results identify the optimal information-theoretic cost of distributed Choi overlap estimation and clarify the role of public classical randomness in distributed
quantum channel learning.
Read the full abstract ▾
All authors Congcong Zheng, Kun Wang, Xutao Yu, Ping Xu, Zaichen Zhang
Quantum Physics
Shot and Architecture Adaptive Subspace Variational Quantum Eigensolver for Microwave Simulation
Zhixiu Han, Fanxu Meng, Weidong Li et al. (+2 more)
Quantum computing offers a promising paradigm for electromagnetic eigenmode analysis, enabling compact representations of complex field interactions and potential exponential speedup over classical numerical solvers. Recent efforts have applied variational
quantum eigensolver (VQE) based methods to compute waveguide modes, demonstrating the feasibility of simulating TE and TM field distributions on noisy intermediate-scale
quantum (NISQ) hardware. However, these studies typically employ manually designed, fixed-depth parameterized
quantum circuits and uniform measurement-shot strategies, resulting in excessive
quantum resource consumption, limited
circuit expressivity, and reduced robustness under realistic noise conditions. To address these limitations, we propose an architecture and shot adaptive subspace variational
quantum eigensolver for efficient microwave waveguide eigenmode simulation on NISQ devices. The proposed framework integrates a reinforcement learning (RL) based
circuit design strategy and an adaptive shot allocation mechanism to jointly reduce
quantum resource overhead. Specifically, the RL
agent autonomously explores the
quantum circuit space to generate hardware-efficient parameterized
quantum circuits, while the adaptive measurement scheme allocates sampling resources according to
Hamiltonian term weights. Numerical experiments on three- and five-
qubit systems demonstrate that the proposed framework achieves accurate estimation of TE and TM mode
eigenvalues, with a minimum absolute error down to $10^{-8}$ and reconstructed field distributions under noiseless conditions in excellent agreement with classical electromagnetic solutions.
Read the full abstract ▾
All authors Zhixiu Han, Fanxu Meng, Weidong Li, Xutao Yu, Zaichen Zhang
Quantum Physics
Robust population transfer by a detuning sign jump: from two-state quantum system to SU(2)-symmetric three-state quantum system
Peter Chernev and Andon A. Rangelov
We propose and analyze a robust population-transfer protocol in a driven two-level system based on a sudden sign change of the detuning at the maximum of a smooth coupling pulse. Away from the jump the dynamics is adiabatic, while the sign flip produces a single nonadiabatic kick in the adiabatic basis. Within a simple stepwise adiabatic-sudden approximation we obtain a compact analytic expression for the final transition probability, identify the parameter regimes that yield high-fidelity inversion, and show that the result depends only on the change of the mixing angle across the detuning jump, i.e., solely on the ratio of the peak Rabi frequency to the detuning. Numerical simulations of the full time-dependent Schrödinger equation confirm the validity and robustness of this description over a broad parameter range. We then use the Majorana decomposition to extend the scheme to an SU(2)-symmetric three-state chain driven by the same coupling and detuning functions. In this setting the three-state propagator is expressed in closed form through the two-level Cayley-Klein parameters, which allows us to derive explicit transition probabilities for all three initial states. In particular, we show that for strong coupling the protocol yields almost complete population transfer between the two outer states, with only small transient population of the middle state, while retaining the same intrinsic robustness as in the underlying two-level model.
Read the full abstract ▾
Quantum Physics · Cross-listed from math.OA
Entanglement in C$^*$-algebras: tensor products of state spaces
Magdalena Musat and Mikael Rørdam
We analyze the Namioka-Phelps minimal and maximal tensor products of compact convex sets which arise as the state spaces of unital C$^*$-
algebras. Relatedly, we study
entanglement in (infinite dimensional) C$^*$-
algebras. While the minimal Namioka-Phelps tensor product of the state spaces of two C$^*$-
algebras is the well-known set of separable (= un-entangled) states on the (minimal) tensor product of the C$^*$-
algebras, we also describe the more elusive maximal Namioka-Phelps tensor product of state spaces of C$^*$-
algebras. We show that the minimal and maximal tensor products of state spaces of C$^*$-
algebras agree precisely when one of the two C$^*$-
algebras is commutative, which confirms Barker's
conjecture in the case where the compact convex sets are state paces of C$^*$-
algebras. Further, the Namioka-Phelps tensor product of the trace simplexes of two or more unital C$^*$-
algebras is shown to be the trace simplex of the (minimal or maximal) tensor product of the C$^*$-
algebras. This enables a systematic way of determining the trace simplex of a tensor product of C$^*$-
algebras.
Read the full abstract ▾
Quantum Physics
Ising on the donut: Regimes of topological quantum error correction from statistical mechanics
Lucas H. English, Sam Roberts, Stephen D. Bartlett et al. (+2 more)
Utility-scale
quantum computers require
quantum error correcting codes with large numbers of physical
qubits to achieve sufficiently low logical error rates. The performance of
quantum error correction (QEC) is generally predicted through large-scale numerical simulations, used to estimate thresholds, finite-size scaling, and exponential suppression of logical errors below threshold. The connection of QEC to models from statistical mechanics provides an alternative tool for analysing QEC performance. However, predicting the behaviour of these models also requires large-scale numerical simulations, as analytic solutions are not generally known. Here we exploit an exact mapping, from a toric code under bit-flip noise that is post-selected on being syndrome free to the exactly-solvable two-dimensional Ising model on a
torus, to derive an analytic solution for the logical failure rate across its full domain of physical error rates. In particular, this mapping provides closed-form expressions for the logical failure rate in four distinct regimes: the path-counting, below-threshold (ordered), near-threshold (critical), and above-threshold (disordered) regimes. Our framework places a number of familiar and long-standing numerical observations on firm theoretical ground. It also motivates explicit ansatze for the conventional QEC setting of non-post-selected codes whose statistical mechanics mappings involve random-bond disorder. Specifically, we introduce an effective tension model for the below-threshold regime, and a new scaling ansatz for the near-threshold regime, derived from an analysis of the domain wall energy cost distributions. By bridging statistical mechanics theory and
quantum error correction practice, our results offer a new toolkit for designing, benchmarking, and understanding topological codes beyond current computational limits.
Read the full abstract ▾
All authors Lucas H. English, Sam Roberts, Stephen D. Bartlett, Andrew C. Doherty, Dominic J. Williamson
Quantum Physics · Cross-listed from cond-mat.mes-hall
Excitation energies and UV-Vis absorption spectra from INDO/s+ML
Ezekiel Oyeniyi and Omololu Akin-Ojo
The semi-empirical INDO/s method is popular for studies of excitation energies and absorption of molecules due to its low computational requirement, making it possible to make predictions for large systems. However, its accuracy is generally low, particularly, when compared with the typical accuracy of other methods such as time-dependent density functional theory (TDDFT). Here, we present machine learning (ML) models that correct the INDO/s results with negligible increases in the amount of computing resources needed. While INDO/s excitations energies have an average error of about 1.1 eV relative to TDDFT energies, the added ML corrections reduce the error to 0.2 eV. Furthermore, this combination of INDO/s and ML produces UV-Vis absorption spectra that are in good agreement with the TDDFT predictions.
Read the full abstract ▾
Quantum Physics
Quantum Separability Criteria Based on Symmetric Measurements
Yu Lu, Wen Zhou, Meng Su et al. (+3 more)
We propose experimentally feasible separability criteria for bipartite systems based on local symmetric measurements. Through detailed examples, we demonstrate that our criteria can detect
entanglement more effectively compared to existing counterparts. Furthermore,we demonstrate the potential for our results to be generalized to general multipartite systems.
Read the full abstract ▾
All authors Yu Lu, Wen Zhou, Meng Su, Hong-Xing Wu, Shao-Ming Fei, Zhi-Xi Wang
Quantum Physics
Loophole-free Bell-inequality violation between atomic states in cavity-QED systems mediated by hybrid atom-light entanglement
Pei-Zhe Li, Soumyakanti Bose, Hyunseok Jeong et al. (+3 more)
We present a feasible and scalable approach to testing Bell nonlocality and implementing device-independent
quantum key distribution (DI-QKD) between distant atomic states in cavity-based architectures, mediated by hybrid atom-light
entanglement. We develop a full theoretical model that incorporates realistic sources of noise – such as transmission loss, limited light-matter coupling efficiency, and imperfect detection. Our analysis shows that strong Bell-Clauser-Horne-Shimony-Holt (CHSH) violations and secure key generation over tens of kilometers are within reach using current or near-term technology. These results position cavity-based platforms with coherent-state encodings as a promising foundation for future scalable, DI
quantum communication networks.
Read the full abstract ▾
All authors Pei-Zhe Li, Soumyakanti Bose, Hyunseok Jeong, William J. Munro, Kae Nemoto, Nicolò Lo Piparo
Quantum Physics
On the Optimality of a Quantum Key Distribution
Georgi Bebrov
Quantum key distribution (QKD) systems require optimal performance of both
quantum and classical channels - utilizing as few as possible
qubits and bits for establishing as many as possible key bits. Here we report a way to determine if a
quantum key distribution model (or protocol) operates in an optimal behavior. This is accomplished by introducing a quantity, called optimality, which is the maximum over the total efficiency of a QKD under any circumstances (any values of QKD parameters). The optimality definition is given for the asymptotic operation of a QKD system - when infinitely many
quantum systems are transferred/used in a
quantum key distribution protocol or a
quantum key distribution system is used infinitely many times. A way to attain the optimality is considered\textemdash implementation of a completely efficient QKD system (a combination of capacity-reaching
quantum channel and a completely compressed classical channel) is presented. Optimal versions of BB84-QKD and twin-field QKD are introduced.
Read the full abstract ▾
Quantum Physics
Generation of mechanical cat-like states via optomagnomechanics
Hao-Tian Li, Hong-Bin Wang, Zi-Xu Lu et al. (+1 more)
We propose an optomagnomechanical approach for preparing a cat-like superposition state of mechanical motion. Our protocol consists of two steps and is based on the magnomechanical system where the magnetostrictively induced displacement further couples to an optical cavity mode via radiation pressure. We first prepare a squeezed mechanical state by driving the magnomechanical system with two microwave pulses. We then switch off the microwave drives and send a weak red-detuned optical pulse to the optical cavity to weakly activate the optomechanical anti-Stokes scattering. We show that $k$
phonons can be subtracted from the prepared squeezed thermal state, conditioned on the detection of $k$ anti-Stokes
photons from the cavity output field, which prepares the mechanical motion in a cat-like state. The work provides a new avenue for preparing mechanical superposition states by combining opto- and magnomechanics and may find applications in the study of macroscopic
quantum states and the test of collapse theories.
Read the full abstract ▾
All authors Hao-Tian Li, Hong-Bin Wang, Zi-Xu Lu, Jie Li
Quantum Physics
Optomagnonic generation of entangled travelling fields with different polarizations
Zi-Xu Lu, Huai-Bing Zhu, Xuan Zuo et al. (+1 more)
The optomagnonic coupling between
magnons and optical
photons is an essential component for building remote
quantum networks based on magnonics. Here we show that such a coupling, manifested as the
magnon-induced Brillouin light scattering, can be exploited to entangle two propagating optical fields. The protocol employs two pairs of the whispering gallery modes coupled to the same
magnon mode in a YIG sphere. In each pair a strong pump field is applied to activate either Stokes or anti-Stokes scattering. Due to the
magnon mode involving in the two scattering processes and as a mediation, Stokes and anti-Stokes
photons of different polarizations get entangled. The
entanglement can be extracted by filtering the travelling output fields centered at the Stokes and anti-Stokes sidebands. Optimal conditions are identified under which strong output
entanglement can be achieved.
Read the full abstract ▾
All authors Zi-Xu Lu, Huai-Bing Zhu, Xuan Zuo, Jie Li
Quantum Physics
Improved gap dependence in adiabatic state preparation by adaptive schedule
Xi Guo and Dong An
Adiabatic
quantum computing is a powerful framework for state preparation, while its
evolution time often scales quadratically in the inverse
Hamiltonian spectral gap, leading to sub-optimal computational complexity. In this work, we introduce a nonlinear adaptive strategy for finding the time scheduling function, and show that the gap dependence can be quadratically improved to be inverse linear for a wide range of systems under a mild gap measure condition. Through variational analysis, we further demonstrate the optimality of our schedule for systems with linear gap and the partial optimality for general systems, while we also rigorously show that the commonly used linear schedule is never optimal.
Read the full abstract ▾
Quantum Physics
Tunable discrete quasi-time crystal from a single drive
Xu Feng, Shuo Liu, Shu Chen et al. (+1 more)
The search for exotic temporal orders in
quantum matter, such as discrete quasi-time
crystals (DQTCs), has become an important theme in nonequilibrium physics. However, realizing these phases has so far required complex protocols, such as drives with multiple incommensurate frequencies. Here, we present a significantly simpler mechanism: the emergence of DQTCs in a dissipative collective
spin system subjected to only a single periodic drive. Remarkably, the characteristic frequencies of this novel phase are not fixed but can be continuously tuned by varying the strength of the drive. Even more strikingly, this tunability is punctuated by Arnold tongues, within which the response main frequency locks to rational fractions of the drive. Our model further provides a unified framework that also encompasses stationary, discrete time
crystals and chaotic phases. This discovery simplifies the requirements for generating complex temporal orders and opens a viable route towards the experimental control and manipulation of quasi-time crystalline matter.
Read the full abstract ▾
All authors Xu Feng, Shuo Liu, Shu Chen, Shi-Xin Zhang
Quantum Physics
Gradient projection method and stochastic search for some optimal control models with spin chains. II
Oleg V. Morzhin
This article (II) continues the research described in [Morzhin O.V. Gradient projection method and
stochastic search for some optimal control models with
spin chains. I (submitted)] (Article I), derives the needed finite-dimensional gradients corresponding to the infinite-dimensional gradients obtained in Article I, both for transfer and keeping problems at a certain $N$-dimensional
spin chain, and correspondingly adapts a projection-type condition for optimality, gradient projection method (GPM). For the case $N=3$, the given in this article examples together with Example 3 in Article I show that: a) the adapted GPM and genetic
algorithm (GA) successfully solved numerically the considered transfer and keeping problems; b) the two- and three-step GPM forms significantly surpass the one-step GPM. Moreover, GA and a special class of controls were successfully used in such the transfer problem that $N=20$ and the final time is not assigned.
Read the full abstract ▾
Quantum Physics
Single-molecule Scale Nuclear Magnetic Resonance Spectroscopy using a Robust Near-Infrared Spin Sensor
Yu Chen, Qi Zhang, Yuanhong Teng et al. (+6 more)
Nuclear magnetic resonance (NMR) at the single-molecule level with atomic resolution holds transformative potential for structural biology and surface chemistry. Near-surface solid-state
spin sensors with optical readout ability offer a promising pathway toward this goal. However, their extreme proximity to target molecules demands exceptional robustness against surface-induced perturbations. Furthermore, life science applications require these sensors to operate in biocompatible spectral ranges that minimize photodamage. In this work, we demonstrate that the PL6
quantum defect in 4H silicon carbide (4H-SiC) can serve as a robust near-infrared
spin sensor. This sensor operates at tissue-transparent wavelengths and exhibits exceptional near-surface stability even at depth of 2 nm. Using shallow PL6 centers, we achieve nanoscale NMR detection of
proton ($\mathrm{^{1}H}$)
spins in immersion oil and fluorine ($\mathrm{^{19}F}$)
spins in Fomblin, attaining a detection volume of $\mathrm{(3~nm)^3}$ and a sensitivity reaching the requirement for single-
proton spin detection. This work establishes 4H-SiC
quantum sensors as a compelling platform for nanoscale
magnetic resonance, with promising applications in probing low-dimensional water phases,
protein folding dynamics, and molecular interactions.
Read the full abstract ▾
All authors Yu Chen, Qi Zhang, Yuanhong Teng, Chihang Luo, Zhijie Li, Jinpeng Liu, Ya Wang, Fazhan Shi, Jiangfeng Du
Quantum Physics
Quantum relaxometry for detecting biomolecular interactions with single NV centers
Min Li, Qi Zhang, Xi Kong et al. (+14 more)
The investigation of biomolecular interactions at the single-molecule level has emerged as a pivotal research area in life science, particularly through optical, mechanical, and electrochemical approaches.
Spins existing widely in biological systems, offer a unique degree of freedom for detecting such interactions. However, most previous studies have been largely confined to ensemble-level detection in the
spin degree. Here, we developed a molecular interaction analysis method approaching single-molecule level based on relaxometry using the
quantum sensor, nitrogen-vacancy (NV) center in diamond. Experiments utilized an optimized diamond surface functionalized with a polyethylenimine nanogel layer, achieving $\sim$10 nm average
protein distance and mitigating interfacial steric hindrance. Then we measured the strong interaction between streptavidin and
spin-labeled biotin complexes, as well as the weak interaction between bovine serum albumin and biotin complexes, at both the micrometer scale and nanoscale. For the micrometer-scale measurements using ensemble NV centers, we re-examined the often-neglected fast relaxation component and proposed a relaxation rate evaluation method, substantially enhancing the measurement sensitivity. Furthermore, we achieved nanoscale detection approaching single-molecule level using single NV centers. This methodology holds promise for applications in molecular screening, identification and kinetic studies at the single-molecule level, offering critical insights into molecular function and activity mechanisms.
Read the full abstract ▾
All authors Min Li, Qi Zhang, Xi Kong, Sheng Zhao, Bin-Bin Pan, Ziting Sun, Pei Yu, Zhecheng Wang, Mengqi Wang, Wentao Ji, Fei Kong, Guanglei Cheng, Si Wu, Ya Wang, Sanyou Chen, Xun-Cheng Su, Fazhan Shi
Quantum Physics
Catalytic Tomography of Ground States
Chi-Fang Chen and Robbie King
We introduce a simple protocol for measuring properties of a gapped ground state with essentially no disturbance to the state. The required
Hamiltonian evolution time scales inversely with the spectral gap and target precision (up to logarithmic factors), which is optimal. For local observables on geometrically local systems, the protocol only requires
Hamiltonian evolution on a quasi-local patch of inverse-gap radius. Our results show that gapped ground states are algorithmically readable from a single copy without a recovery or rewinding procedure, which may drastically reduce
tomography overhead in certain
quantum simulation tasks.
Read the full abstract ▾
Quantum Physics
Integrated Generation and Purification of Entangled Coherent States for Non-Gaussian Teleportation
Ananga Mohan Datta, William J. Munro, Nicolo Lo Piparo et al. (+1 more)
Entangled coherent states (ECS) provide a powerful non-Gaussian resource for continuous-variable
quantum communication, but their generation in scalable architectures remains challenging. We propose an integrated photonic scheme that creates high-fidelity ECS from a two-mode squeezed
vacuum via
photon subtraction in a symmetric waveguide trimer. The resulting non-Gaussian
entanglement is further enhanced by single-
photon catalysis, which purifies the distributed state after transmission through lossy channels. Using these purified ECS resources, we analyze a
photon-number-based teleportation protocol and demonstrate high-fidelity transfer of both coherent states and Schrodinger cat states. In particular, the teleportation fidelity for cat states exceeds the classical threshold of 2/3 over a broad range of realistic channel and squeezing parameters, whereas Gaussian resources fail to do so. Our results show that integrated
photon subtraction and catalysis enable practical, chip-compatible generation of non-Gaussian
entanglement suitable for advanced
quantum teleportation and continuous-variable
quantum networks.
Read the full abstract ▾
All authors Ananga Mohan Datta, William J. Munro, Nicolo Lo Piparo, Kae Nemoto
Quantum Physics · Cross-listed from physics.atom-ph
Search for a solar-bound axion halo using the Global Network of Optical Magnetometers for Exotic physics searches
Tatum Z. Wilson, Derek F. Jackson Kimball, Samer Afach et al. (+50 more)
We report on a search for a gravitationally bound
solar axion halo using data from the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), a worldwide array of magnetically shielded atomic magnetometers with sensitivity to exotic
spin couplings. Motivated by recent theoretical work suggesting that self-interacting ultralight
axions can be captured by the Sun's gravitational field and thermalize into the ground state, we develop a signal model for the pseudo-
magnetic fields generated by
axion-
proton gradient couplings in such a
halo. The analysis focuses on the fifth GNOME Science Run (69 days, 12 stations), employing a cross-correlation pipeline with time-shifted daily modulation templates to search for the global, direction-dependent, monochromatic signal expected from a
solar axion halo. No statistically significant candidate signals are observed. We set 95% confidence-level upper limits on the amplitude of the
axion-induced pseudo-
magnetic field over the frequency range $\approx 0.05-20$ Hz, translating to constraints on the linear and quadratic
axion-
proton couplings for
halo densities predicted by gravitational capture models and for the maximum overdensities allowed by planetary ephemerides. In the quadratic coupling case, our limits surpass existing astrophysical bounds by over two orders of magnitude across much of the accessible parameter space.
Read the full abstract ▾
All authors Tatum Z. Wilson, Derek F. Jackson Kimball, Samer Afach, Jiexiao Bi, B. C. Buchler, Dmitry Budker, Kaleb Cervantes, Joshua Eby, Nataniel L. Figueroa, Ron Folman, Jiawei Gao, Daniel Gavilán-Martín, Menachem Givon, Zoran D. Grujić, Hong Guo, Paul Hamilton, M. P. Hedges, Zhejun Huang, Dongok Kim, Younggeun Kim, Sami S. Khamis, Emmanuel Klinger, Abaz Kryemadhi, Nina Kukowski, Jianjun Li, Grzegorz Lukasiewicz, Hector Masia-Roig, Tafai Muck, Michal Padniuk, Christopher A. Palm, Chaitanya Paranjape, Sun Yool Park, Xiang Peng, Gilad Perez, Rayshaun Preston, Szymon Pustelny, Wolfram Ratzinger, Yossi Rosenzweig, Ophir M. Ruimi, Amy Saputo, Theo Scholtes, P. C. Segura, Yannis K. Semertzidis, Yun Chang Shin, Jason E. Stalnaker, Ibrahim Sulai, Dhruv Tandon, Rayshaun Thompson, Ken Vu, Arne Wickenbrock, Teng Wu, Yucheng Yang, Yixin Zhao
Quantum Physics
Generating strong mechanical squeezing via combined squeezed vacuum field and two-tone driving
Xiao-Jie Wu, Huan-Huan Cheng, Cheng-Hua Bai et al. (+1 more)
We propose a novel scheme for generating mechanical squeezed states based on the combined mechanism of a two-tone driving and a squeezed
vacuum field. This innovative approach achieves a remarkable improvement in mechanical squeezing performance across the entire range of red/blue detuning ratios. Our study reveals that the squeezed
vacuum field not only induces position squeezing of the mechanical oscillator but also facilitates momentum squeezing through phase matching. Moreover, the total squeezing degree exhibits nonlinear enhancement with the increasing of squeezing parameter $r$. The mechanical squeezed state exhibits a $2\pi$-periodic dependence in relation to the squeezing phase $\theta$, offering experimental implementation with a high degree of operational flexibility. Notably, the scheme exhibits strong robustness against cavity dissipation and environmental thermal noise, substantially relaxing the strict parameter-matching requirements inherent in conventional approaches.
Read the full abstract ▾
All authors Xiao-Jie Wu, Huan-Huan Cheng, Cheng-Hua Bai, Shao-Xiong Wu
Quantum Physics
Optimal learning of quantum channels in diamond distance
Antonio Anna Mele and Lennart Bittel
Quantum process
tomography, the task of estimating an unknown
quantum channel, is a central problem in
quantum information theory. A long-standing open question is how many uses of an unknown channel are required to learn it in diamond distance, the standard metric for distinguishing
quantum processes. While
quantum state
tomography is well understood, for general channels the problem remained open beyond the
unitary case. Here we establish the query complexity of channel
tomography with optimal dependence on the dimension parameters, at any fixed constant accuracy. We design an
algorithm showing that any channel with input/output dimensions $d_{\mathrm{in}},d_{\mathrm{out}}$ and Kraus rank at most $k$ can be learned to accuracy $\varepsilon$ using $O(d_{\mathrm{in}}d_{\mathrm{out}}k/\varepsilon^{2})$ channel uses. Conversely, we prove that $\Omega(d_{\mathrm{in}}d_{\mathrm{out}}k)$ uses are necessary at constant accuracy and that, for non-minimal Kraus rank, a separate $\Omega(1/\varepsilon^{2})$ contribution is unavoidable. Since channels subsume states,
unitaries, isometries, and measurements as special cases, our protocol provides a unified framework for these
tomography tasks, yielding new guarantees for isometry and measurement
tomography while recovering known optimal scalings for state and
unitary tomography. Our
algorithm follows the natural strategy of performing optimal
tomography on the Choi state. The main technical contribution is to show that this suffices to control the induced diamond-distance error, avoiding the dimension loss incurred by a naive conversion from Choi-state trace distance to channel diamond distance. The protocol uses the channel non-adaptively to prepare Choi-state copies, purifies them in parallel, and performs optimal pure-state
tomography on the resulting purifications. Hence, we reduce channel
tomography to pure-state
tomography.
Read the full abstract ▾
Quantum Physics
Entropic Uncertainty Relations with Quantum Memory in Accelerated Frames via Unruh-DeWitt Detectors
Ming-Ming Du, Hong-Wei Li, Shu-Ting Shen et al. (+5 more)
Quantum uncertainty is deeply linked to
quantum correlations and relativistic motion. The entropic uncertainty relation with
quantum memory offers a powerful way to study how shared
entanglement affects measurement precision. However, under acceleration, the Unruh effect can degrade
quantum correlations, raising questions about the reliability of QMA-EUR in such settings. Here, we investigate the QMA-EUR for two uniformly accelerating Unruh-DeWitt detectors coupled to a massless scalar field. Using the Kossakowski-Lindblad master equation, we calculate the entropic uncertainty, its lower bound, and the tightness of the relation under different Unruh temperatures. We find that acceleration does not always increase the lower bound on the uncertainty relation. Depending on the initial correlations between the detectors, it may either increase or decrease. This behavior results from the interplay between
quantum discord and minimal missing information. Interestingly, a higher
quantum discord does not necessarily lead to lower uncertainty.
Read the full abstract ▾
All authors Ming-Ming Du, Hong-Wei Li, Shu-Ting Shen, Xiao-Jing Yan, Xi-Yun Li, Lan Zhou, Wei Zhong, Yu-Bo Sheng
Quantum Physics
Photorefractive-based on-chip optical power limiter against light-injection attacks in quantum key distribution
Min Chen, Hong-Yan Song, Jia-Lin Chen et al. (+10 more)
Light-injection attacks pose critical security threats to
quantum key distribution (QKD) systems. Conventional countermeasures, such as isolators, filters, and optical power monitoring, suffer from limited on-chip compatibility and inherent security vulnerabilities. To overcome these limitations, we propose and experimentally demonstrate an integrated attack sensing and automatic response unit utilizing the photorefractive effect in a thin-film lithium niobate microring resonator. The unit provides a rejection ratio exceeding 25 dB against non-resonant injected light. Under resonant attacks with power levels above tens of microwatts, the unit autonomously attenuates the signal transmission, with 14 dB attenuation measured at the maximum tested attack power of 10 dBm, leading to a significant suppression of the secure key rate. We further verify its response to pulsed light injection and incorporate possible residual leakage associated with finite response time into the key-rate analysis. This work provides a highly sensitive, broadband, and fully on-chip defense mechanism that significantly enhances the physical-layer security of QKD systems against light-injection attacks.
Read the full abstract ▾
All authors Min Chen, Hong-Yan Song, Jia-Lin Chen, Peng Ye, Guo-Wei Zhang, Fang-Xiang Wang, Li Zhang, Shuang Wang, De-Yong He, Zhen-qiang Yin, Guang-Can Guo, Wei Chen, Zheng-Fu Han
Quantum Physics
Quantum Internet in the Sky: Vision, Challenges, Solutions, and Future Directions
Phuc V. Trinh and Shinya Sugiura
This article envisions the concept of a “
Quantum Internet in the Sky", aiming to establish ubiquitous
quantum communication links among distant nodes via free-space optical channels. Our key focus is on deploying
quantum communication terminals on non-terrestrial platforms, specifically unmanned aerial vehicles and satellites, at various altitudes. By highlighting the unique characteristics of these platforms compared to terrestrial counterparts, we address inherent challenges and discuss potential solutions through meticulous system designs and analyses of typical non-terrestrial
quantum communication scenarios. Finally, we illuminate the path forward by proposing essential future directions that underscore the integration of high-dimensional multipartite
quantum communications with sensing, computing, and intelligence for multiple users en route to realizing a fully operational
Quantum Internet.
Read the full abstract ▾
Quantum Physics
Simultaneous Classical and Quantum Communications: Recent Progress and Three Challenges
Phuc V. Trinh, Shinya Sugiura, Carlo Ottaviani et al. (+2 more)
A critical aspect of next-generation wireless networks is the integration of
quantum communications to guard against
quantum computing threats to classical networks. Despite successful experimental demonstrations, integrating
quantum communications into the classical infrastructure faces substantial challenges, including high costs, compatibility issues, and extra hardware deployment to accommodate both classical and
quantum communication equipment. To mitigate these challenges, we explore novel protocols that enable simultaneous classical and
quantum communications, relying on a single set of transceivers to jointly modulate and decode classical and
quantum information onto the same signal. Additionally, we emphasize extending
quantum communication capabilities beyond traditional optical bands into the terahertz, even possibly to millimeter-wave and microwave frequencies, thereby broadening the potential horizon of
quantum-secure applications. Finally, we identify open problems that must be addressed to facilitate practical implementation.
Read the full abstract ▾
All authors Phuc V. Trinh, Shinya Sugiura, Carlo Ottaviani, Chao Xu, Lajos Hanzo
Quantum Physics
Eight-Qubit Operation of a 300 mm SiMOS Foundry-Fabricated Device
Andreas Nickl, Nard Dumoulin Stuyck, Paul Steinacker et al. (+24 more)
Silicon
spin qubits are a promising platform for
quantum computing due to their high coherence, controllability, and CMOS manufacturability, yet scalable implementations have so far been limited to a few
qubits. Here, to take a step towards larger
qubit systems, we tune and coherently control an eight-dot linear array of silicon
spin qubits fabricated in a 300~mm CMOS-compatible foundry process, establishing operational scalability beyond the two-
qubit regime. All eight
qubits are successfully tuned and characterized as four double-dot pairs, exhibiting Ramsey dephasing times $T_2^*$ up to 41(2)$~\mu$s and Hahn-echo coherence times $T_2^{\mathrm{Hahn}}$ up to 1.31(4)$~$ms. Readout of the central four
qubits is achieved via a cascaded charge-sensing protocol, enabling high-fidelity measurements of the entire multi-
qubit array in a two step process. Additionally, we demonstrate a two-
qubit gate operation between adjacent
qubits with low phase noise. We show that silicon
spin qubit arrays can be scaled to medium-sized arrays of 8
qubits while maintaining system coherence.
Read the full abstract ▾
All authors Andreas Nickl, Nard Dumoulin Stuyck, Paul Steinacker, Jesus D. Cifuentes, Santiago Serrano, MengKe Feng, Ensar Vahapoglu, Fay E. Hudson, Kok Wai Chan, Stefan Kubicek, Julien Jussot, Yann Canvel, Sofie Beyne, Yosuke Shimura, Roger Loo, Clement Godfrin, Bart Raes, Sylvain Baudot, Danny Wan, Arne Laucht, Chih-Hwan Yang, Wee Han Lim, Andre Saraiva, Christopher C. Escott, Kristiaan De Greve, Andrew S. Dzurak, Tuomo Tanttu