Quantum Physics
Scalable on-chip integration of diamond color centers for cryogenic quantum photonics
H. Kurokawa, K. Sato, M. Kamata et al. (+16 more)
Chip integration of
quantum emitters is a crucial milestone for scalable
quantum photonic information processing. Among optically active defect centers for
quantum photonics, diamond color centers are promising because of their long
spin coherence times and high
photon emission rates. However, for a coherent-
photon emission, they typically require a cryogenic environment to protect optical coherence from thermal
phonons, which makes chip integration challenging. In this paper, we develop a chip-integrated diamond photonic
crystal cavity
embedding an ensemble of nitrogen-vacancy (NV) centers. We confirm cryogenic operation by observing Purcell enhancement of NV-center emission via an edge-coupled optical fiber. This result demonstrates successful integration of diamond color centers, a photonic
crystal cavity, and an optical waveguide-fiber package, representing a key step toward scalable diamond-based
quantum communication platforms.
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All authors H. Kurokawa, K. Sato, M. Kamata, S. Ishida, H. Matsukiyo, N. Pholsen, M. Nishioka, S. Ji, H. Otsuki, S. Hachuda, M. Kunii, T. Tamanuki, K. Kimura, K. Takenaka, Y. Sekiguchi, S. Onoda, S. Iwamoto, T. Baba, H. Kosaka
Quantum Physics · Cross-listed from cond-mat.mes-hall
Tensor-network simulation of quantum transport in many-quantum-dot systems
Maximilian Streitberger and Marko J. Rančić
Transport through correlated nanoscale systems underpins the operation of
quantum-dot and molecular-scale devices, yet accurate simulations of large open
quantum systems remain computationally challenging as system size increases. Tensor-network methods offer a promising route past this scaling barrier by efficiently compressing
quantum states. Here we extend a tensor-based solver with a jump-counting
estimator that enables direct computation of steady-state electron currents from lead-induced tunneling events. We
benchmark the resulting currents against the state-of-the-art master-equation solver QmeQ across a range of lead-dot and inter-dot coupling parameters and find quantitative agreement in the tractable regime. Compared with classical approaches, TJM reduces
memory requirements and wall-clock time by orders of magnitude, enabling simulations of interacting
quantum-dot arrays far beyond the range accessible to density-
matrix-based transport solvers and systematic studies of size-dependent nonequilibrium transport in larger arrays. Our approach allow us to model
quantum transport in an array of up to fifty (50)
quantum dots.
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Quantum Physics
Quantum MIMO Channel Modeling in Turbulent Free-Space Optical Links
Heyang Peng, Seid Koudia, Semih Oktay et al. (+2 more)
Free-space optical (FSO) links supporting spatial multiplexing provide a natural physical realization of
Quantum MIMO channels. We develop a first-principles model for
Quantum MIMO channels derived directly from wave-optical propagation through three-dimensional atmospheric
turbulence. The framework explicitly accounts for intermodal crosstalk, finite detection apertures, and the system-bath separation induced by spatial-mode projection. We distinguish between distinguishable and indistinguishable
photon regimes, showing that indistinguishability leads to intrinsically many-body interference effects described by
matrix permanents. To obtain a completely positive and trace-preserving logical description, we introduce an erasure-extended encoding in which
turbulence-induced leakage and
photon loss are mapped to flagged erasure states. The resulting
Quantum MIMO channel naturally reduces to a correlated n-
qubit erasure channel, with correlations arising from the shared turbulent medium. Limiting regimes in which correlated Pauli channels emerge as effective approximations are also identified.
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All authors Heyang Peng, Seid Koudia, Semih Oktay, Mert Bayraktar, Symeon Chatzinotas
Quantum Physics · Cross-listed from cond-mat.str-el
A Practical Introduction to Tensor Network Renormalization with TNRKit.jl
Victor Vanthilt, Adwait Naravane, Chenqi Meng et al. (+1 more)
We present TNRKit, an open-source Julia package for Tensor Network Renormalization (TNR) of two- and three-dimensional classical statistical models and Euclidean
lattice field theories. Built on top of TensorKit, it provides a
symmetry-aware framework for constructing tensor-network representations of partition functions and coarse-graining them using methods such as TRG, HOTRG, and LoopTNR. Beyond thermodynamic quantities, the package enables the extraction of universal conformal data – including scaling dimensions and the central charge – directly from fixed-point tensors. TNRKit is designed with both usability and extensibility in mind, offering a practical platform for applying, benchmarking, and developing modern tensor renormalization
algorithms. This paper also serves as a self-contained introduction to the TNR framework.
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All authors Victor Vanthilt, Adwait Naravane, Chenqi Meng, Atsushi Ueda
Quantum Physics
Sayantan Roy, Atin Gayen, Aditi Kar Gangopadhyay et al. (+1 more)
Most
quantum divergences derive their structure from classical f-divergences or Renyi-type constructions, a dependence that obscures several
quantum geometric effects. We introduce a
quantum relative-alpha-
entropy that extends Umegaki's relative
entropy while falling outside the f-divergence class. The proposed divergence exhibits a nonlinear convexity property, which yields a generalized convexity result for the Petz-Renyi divergence for alpha greater than one, complementing the known convexity for alpha less than one. It is additive under tensor products, invariant under
unitary transformations, and depends only on the relative geometry of
quantum states rather than their absolute magnitudes. Using Nussbaum-Szkola-type distributions, we also establish an exact correspondence of this divergence with classical relative-alpha-
entropy. This reveals relative-alpha-
entropy as a fundamentally
geometric notion of
quantum distinguishability not captured by existing divergence frameworks.
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All authors Sayantan Roy, Atin Gayen, Aditi Kar Gangopadhyay, Sugata Gangopadhyay
Quantum Physics
Emergence of Non-Markovian Classical-Quantum Dynamics from Decoherence
Shogo Tomizuka and Hiroki Takeda
The
quantum nature of
gravity remains experimentally unverified, despite recent proposals to probe it using tabletop experiments such as
gravity-mediated
entanglement schemes. In parallel, consistent formulations of classical–
quantum dynamics have been developed as alternative descriptions of
gravity, in which
quantum matter interacts with a classical mediator assumed to be fundamentally classical. In this work, we show that classical–
quantum dynamics arise generically as an effective description of fully
quantum systems under decoherence, providing a bridge between fully
quantum and classical–
quantum dynamics. We derive the reduced dynamics, which are generically non-Markovian, using an explicit hidden model in which the mediator is coupled to unobserved environmental degrees of freedom. We identify a concrete criterion for when a classical–
quantum interpretation is valid: the semi-Wigner operator associated with the mediator sector must remain positive semidefinite, which can be expressed as a positivity condition on nonlocal kernels governing the
evolution. In the short-
memory limit, the reduced
evolution reproduces Markovian classical–
quantum dynamics of Oppenheim and collaborators. Our results imply that a classical mediator can arise effectively from decohered
quantum dynamics, so that experimental agreement with classical-
quantum models does not uniquely determine whether the mediator is fundamentally classical.
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Quantum Physics · Cross-listed from cond-mat.mes-hall
Millisecond spin relaxation times of distinct electron and hole subensembles in MA$_x$FA$_{1-x}$PbI$_3$ perovskite crystals
Rongrong Hu, Sergey R. Meliakov, Dmitri R. Yakovlev et al. (+4 more)
The unique combination of outstanding optical quality and attractive
spin properties opens new avenues for optical
spin control in hybrid organic-inorganic perovskite
semiconductors. Using the optically detected
magnetic resonance technique, we study the
spins of electrons and holes in mixed-cation MA$_x$FA$_{1-x}$PbI$_3$ single
crystals with $x = 0.4$ and 0.8. Multiple distinct
spin subensembles with $g$-factors spanning from 2.9 to 3.6 for electrons and from 0.5 to 1.2 for holes are resolved, revealing diverse localization environments. We measure the longitudinal
spin relaxation times, $T_1$, reaching 2 ms and remaining in the $\mu$s range even for weakly localized carriers at the cryogenic temperature of 1.6 K. The
magnetic-field dependence of $T_1$ is dominated by the random
nuclear (Overhauser) fields with strengths of $\sim 0.4-0.8$ mT for electrons and $\sim 4-12$ mT for holes, corresponding to $\mu$s-long correlation times of the hyperfine field determined by carrier hopping between shallow localization sites. The temperature dependence of $T_1$ reveals a weak localization potential of the charge carriers and shows a correlation between $T_1$ and the inhomogeneity of the
spin ensemble. These results establish mixed-A-site perovskite single
crystals as a promising solid-state platform with long-lived
spin states for
quantum information applications.
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All authors Rongrong Hu, Sergey R. Meliakov, Dmitri R. Yakovlev, Bekir Turedi, Maksym V. Kovalenko, Manfred Bayer, Vasilii V. Belykh
Quantum Physics · Cross-listed from cond-mat.mes-hall
Telecom C-band single-photon sources with a semiconductor-dielectric microresonator
Yuriy Serov, Aidar Galimov, Sergey Sorokin et al. (+19 more)
Secure communications with
quantum key distribution over fiber-optic links is one of the few recognized applications of
quantum physics at the level of individual quanta – single C-band
photons. Currently, the widely used sources of such
photons are highly attenuated
laser pulses, featured by a low probability of single
photon occurrence. Here, we present an efficient source with an InAs/GaAs
quantum dot on a metamorphic buffer layer inside a micropillar-shaped microcavity. The key innovation is the use of different
semiconductor and dielectric materials to form the lower (GaAs/AlGaAs) and upper (Si/SiO$_2$) Bragg reflectors. Compatibility of these materials in a monolithic source is achieved by depositing a small amount of Si/SiO$_2$ pairs on an incomplete micropillar made from a coherent
heterostructure grown by molecular beam epitaxy. This design enables resonant excitation with $\pi$-pulses and generation of polarized
photons with a record-breaking end-to-end efficiency of 11%.
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All authors Yuriy Serov, Aidar Galimov, Sergey Sorokin, Nikolai Maleev, Marina Kulagina, Yuriy Zadiranov, Grigorii Klimko, Maxim Rakhlin, Alexey Veretennikov, Gleb Veyshtort, Olga Lakuntsova, Yuliya Salii, Daria Berezina, Sergey Troshkov, Demid Kirilenko, Alexey Blokhin, Alexei Vasil'ev, Alexander Kuzmenkov, Mikhail Bobrov, Irina Sedova, Tatiana V. Shubina, Alexey A. Toropov
Quantum Physics
A hardware efficient quantum residual neural network without post-selection
Amena Khatun, Akib Karim and Muhammad Usman
We propose a hardware efficient
quantum residual neural network which implements residual connections through a deterministic mixture of the identity operation and variational
unitaries, enabling fully differentiable training. In contrast to the previous implementation of residual connections, our architecture avoids post-selection while preserving residual learning. Furthermore, we highlight
circuit constructions where barren plateaus could be mitigated, which are considered as a major limitation of variational
quantum learning models. In order to show the working of our model, we report its application to image classification tasks by training it for MNIST, CIFAR, and SARFish
datasets, achieving accuracies of 99% and 80% for binary and multi-class classifications, respectively. These accuracies are comparable to previously achieved from the standard variational models, however our model requires 10x fewer gates making it better suited for resource constraint near-term
quantum processors. In addition to high accuracies, the proposed architecture also demonstrates
adversarial robustness which is another desirable parameter for
quantum machine learning models. Overall our architecture offers a new pathway for developing accurate, robust, trainable and hardware efficient
quantum machine learning models.
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Quantum Physics
Perturbative hydrogenic Lamb shifts and radiative decay rates – an so(4,2)-based algebraic approach
Gernot Alber
It is shown that algebraic techniques based on the Lie
algebra so(4,2) provide efficient tools for evaluating Lamb shifts and radiative decay rates for hydrogenic energy eigenstates as they systematically exploit the intrinsic
symmetry of the hydrogenic
Hamiltonian. As a main result in lowest order perturbation theory with respect to the fine-structure constant integral representations are derived for the complex-valued energy shifts of hydrogen-like ions from which Lamb shifts and radiative decay rates can be evaluated in a unified way, thus generalizing a recently discussed algebraic approach of Maclay. In order to exemplify the usefulness of this algebraic approach numerical results are presented for Lamb shifts and radiative decay rates which transcend the dipole approximation and contain the dipole approximation as a limiting case.
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Quantum Physics · Cross-listed from cs.NI
Towards National Quantum Communication in Europe: Planning and Sizing Terrestrial QKD Networks
Sebastian Raubitzek, Werner Strasser, Sebastian Ramacher et al. (+3 more)
The European Union is developing the European
Quantum Communication Infrastructure (EuroQCI) as a pan-European network to provide secure communication capabilities across Member States, including governmental and critical-infrastructure domains. While the strategic objective is defined at EU level, the required scale and structure of national
quantum key distribution (QKD) networks remain largely unspecified. This work addresses the question of how to plan and size national terrestrial QKD networks to support critical infrastructure and public authorities. We propose a reproducible planning methodology that estimates network size, total fiber length, and the number of required QKD components based on a small set of explicit assumptions. The approach is demonstrated for Austria, where a synthetic but structured network model is constructed and evaluated using Monte Carlo simulation. The model focuses on terrestrial QKD infrastructure and explicitly excludes space-based segments. It estimates endpoint counts, trusted repeater node requirements, and hop-length distributions under realistic operational constraints. The Austrian case is then used as a baseline to derive scaling rules for other EU Member States based on population and geographic extent. The results provide first-order planning estimates for national QKD backbone sizes across Europe. These estimates are not intended as deployment designs but as planning-level references that support early-stage cost assessment and infrastructure dimensioning under the EuroQCI framework.
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All authors Sebastian Raubitzek, Werner Strasser, Sebastian Ramacher, Thomas Lebeth, Andreas Neuhold, Christoph Pacher
Quantum Physics · Cross-listed from hep-lat
Quantum simulation of baryon scattering in SU(2) lattice gauge theory
João Barata, Juan Hormaza, Zhong-Bo Kang et al. (+1 more)
We present a first real-time study of hadronic scattering in a $(1+1)$-dimensional SU(2)
lattice gauge theory with fundamental
fermions using tensor-network techniques. Working in the gaugeless
Hamiltonian formulation, we investigate scattering processes across sectors of fixed global
baryon number $B = 0, 1, 2$, corresponding respectively to
meson–
meson,
meson–
baryon, and
baryon–
baryon collisions. At strong coupling, the $B = 0$ and $B = 2$ channels exhibit predominantly elastic dynamics closely resembling the U(1) Schwinger model. The mixed $B = 1$ sector displays qualitatively new behavior:
meson and
baryon wavepackets become entangled during the collision, with the slower state becoming spatially delocalized while the faster one propagates ballistically. We characterize these processes through local observables,
entanglement entropy, and the information
lattice.
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All authors João Barata, Juan Hormaza, Zhong-Bo Kang, Wenyang Qian
Quantum Physics · Cross-listed from cs.CR
Broken Quantum: A Systematic Formal Verification Study of Security Vulnerabilities Across the Open-Source Quantum Computing Simulator Ecosystem
Dominik Blain
Quantum computing simulators form the classical software foundation on which virtually all
quantum algorithm research depends. We present Broken
Quantum, the first comprehensive formal security audit of the open-source
quantum computing simulator ecosystem. Applying COBALT QAI – a four-module static analysis engine backed by the Z3 SMT solver – we analyze 45 open-source
quantum simulation frameworks from 22 organizations spanning 12 countries. We identify 547 security findings (40 CRITICAL, 492 HIGH, 15 MEDIUM) across four vulnerability classes: CWE-125/190 (C++
memory corruption), CWE-400 (Python resource exhaustion), CWE-502/94 (unsafe deserialization and code injection), and CWE-77/22 (QASM injection – a novel,
quantum-specific attack vector with no classical analog). All 13 vulnerability patterns are formally verified via Z3 satisfiability proofs (13/13 SAT). The 32-
qubit boundary emerges as a consistent formal threshold in both C++ and Python vulnerability chains. Supply chain analysis identifies the first documented case of vulnerability transfer from a commercial
quantum framework into US national laboratory infrastructure (IBM Qiskit Aer to XACC/Oak Ridge National Laboratory). Nine frameworks score 100/100 under all four scanners; Qiskit Aer,Cirq, tequila, PennyLane, and 5 others score 0/100.
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Quantum Physics · Cross-listed from physics.optics
Attosecond quantum spectroscopy with entangled photon pairs
Zijian Lyu, Fengxiao Sun, Sili Yi et al. (+6 more)
Bright squeezed light from parametric down-conversion in the infrared (IR) frequency range has triggered the emergence of attosecond
quantum optics – a new research field at the interface of
quantum optics, strong-field physics, and attosecond technology. Two challenges arise at this interface: transferring
quantum features of the IR light sources to the ultraviolet (UV) and extreme ultraviolet (XUV) frequency range via strong-field nonlinearities, and exploiting
quantum optical properties of the nonlinear optical response as a new probe in ultrafast dynamics. Here, we address both by driving high-harmonic generation (HHG) in solids with entangled
photon pairs either in degenerate or non-degenerate frequency modes. In the degenerate mode, single-shot measurements of harmonics up to the 10th order reveal strong
photon bunching whose $g^{(2)}$ first grows and then decreases with the harmonic order. We show that this behavior tracks different microscopic mechanisms responsible for harmonic emission, demonstrating the potential of attosecond
quantum optical spectroscopy. In the non-degenerate case, the harmonics retain
quantum-induced correlations, verified by wavelength-resolved second-order cross-correlation maps. Our findings demonstrate transfer of
quantum photon correlations into the XUV domain and open a pathway toward
quantum-enhanced attosecond spectroscopy and control of ultrafast dynamics in solids.
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All authors Zijian Lyu, Fengxiao Sun, Sili Yi, Jingze Li, Haodong Liu, Qiongyi He, Qihuang Gong, Misha Ivanov, Yunquan Liu
Quantum Physics · Cross-listed from physics.atom-ph
Strong-field ionization of atoms with bright squeezed vacuum light
Haodong Liu, Xiaoxiao Long, Peizeng Li et al. (+2 more)
Strong-field ionization is the cornerstone of attosecond physics, which has been extensively studied under coherent-state driving. Recently, the interface between attosecond physics and
quantum optics has emerged as a new frontier. Yet, owing to experimental limitations, the role of the
quantum nature of light in atomic strong-field ionization has remained unexplored. Here, we demonstrate strong-field ionization of xenon atoms driven by bright squeezed
vacuum (BSV) with average pulse energy up to 10 \textmu J. We show that, as a nonclassical state with zero mean field and strong intensity fluctuations, BSV selectively enhances the spider-like
holographic structures in the photoelectron momentum distributions. Using a
quantum-light-corrected
quantum-trajectory Monte Carlo (q-QTMC) model, we attribute this effect to the intrinsic coherence of trajectory pairs emitted within the same subcycle field fluctuation. These dynamically correlated paths exhibit enhanced phase stability and remain robust against dephasing, whereas asynchronous paths are filtered out by field noise. Our results reveal a
quantum-fluctuation-induced mechanism for coherence protection in strong-field processes, positioning BSV as an effective coherence filter and establishing a new regime of
quantum-enabled noise-resilient ultrafast dynamics.
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All authors Haodong Liu, Xiaoxiao Long, Peizeng Li, Zijian Lyu, Yunquan Liu
Quantum Physics · Cross-listed from cond-mat.str-el
Magnon harmonic generation in antiferromagnets: Dynamical symmetry enriched by symmetry breaking
Yuto Jita, Minoru Kanega, Takumi Ogawa et al. (+2 more)
In recent years, techniques of intense THz
laser have enabled us to experimentally observe nonlinear
spin dynamics in antiferromagnets since the elementary excitations such as
magnons reside on a THz to GHz range in antiferromagnets and THz
laser thus can directly excite them. We numerically and theoretically investigate THz-
laser or GHz-wave driven harmonic generations in typical ordered phases of antiferromagnets: Néel, canted and weak
ferromagnetic phases. The radiation waves (harmonic generations) are created by the incident-wave driven
magnon dynamics. We point out that
magnetic orders and phase transitions can change the spectra of harmonic generations, differently from those of metallic,
semiconductor, or atomic-gas systems without (spontaneous)
symmetry breakings. We consider both the
magnon harmonic generation driven by standard single-color
laser and that by two-color
laser in the antiferromagnets, and find several dynamical
symmetries and the corresponding selection rules of the harmonic generations. These results indicate that the
magnon harmonic generation spectra provide new information about
symmetry or
symmetry breaking of antiferromagnets.
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All authors Yuto Jita, Minoru Kanega, Takumi Ogawa, Shunsuke C. Furuya, Masahiro Sato
Quantum Physics
Environment-Assisted Decoherence Suppression of Optical Non-Gaussian States
Akihiro Machinaga, Naoki Aritomi, Ryoga Sakurada et al. (+10 more)
Optical loss is a common bottleneck in photonic
quantum information processing, undermining the
quantum advantage over classical approaches. Although several countermeasures, such as
quantum distillation and error correction, have been proposed, they typically require experimentally demanding non-Gaussian operations. Here, we demonstrate a Gaussian-only scheme that suppresses loss-induced decoherence for general, unknown optical
quantum states. By injecting a squeezed
vacuum state into an environment of the loss channel and performing feedforward based on environmental monitoring, the scheme effectively suppresses loss-induced noise. Our programmable loop-based optical
circuit allows us to implement the scheme for several types of loss-sensitive non-Gaussian states under various loss conditions for up to five steps, and directly compare the results with the unsuppressed case. Our results show that the scheme consistently mitigates state degradation, preserving higher fidelity and Wigner negativity than without suppression. This approach can be applied to mitigating a broad class of errors in optical systems and extending
quantum memory lifetimes. Moreover, it is compatible with other loss-suppression techniques and extendable to physical platforms beyond optics, offering a promising route toward reducing the overhead required for fault-tolerant
quantum information processing.
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All authors Akihiro Machinaga, Naoki Aritomi, Ryoga Sakurada, Daichi Okuno, Keitaro Anai, Takahiro Kashiwazaki, Takeshi Umeki, Shigehito Miki, Masahiro Yabuno, Hirotaka Terai, Petr Marek, Radim Filip, Shuntaro Takeda
Quantum Physics · Cross-listed from physics.optics
Steady-State Statistical Modeling of Digitally Stabilized Laser Frequency with Markov-State Feedback
Swarnav Banik, Elliot Greenwald and Xing Pan
Laser frequency stabilization is conventionally analyzed using continuous-time control theory, which accurately models analog feedback but is insufficient for digital implementations where quantization, sampling, and
stochastic noise shape the dynamics. In modern digital
laser systems, such as Photonic Integrated
Circuit (PIC)-based
lasers, finite discriminator and actuator resolution, sampling delays, and measurement noise introduce
stochastic behavior that deterministic models do not capture. We present a discrete-time Markov-state framework that models the
evolution of the quantized actuator in a digital
laser frequency lock, with state-transition probabilities determined by the frequency discriminator response, noise statistics, and implemented digital control logic. The steady-state actuator and locked-
laser frequency distributions are obtained directly from the unit-
eigenvalue solution of the transition
matrix, providing immediate access to key stability metrics without long time-domain simulations. For white frequency noise, we show that the Markov formulation is exact under decorrelated sampling and update schemes, while correlated discriminator sampling introduces a predictable inflation of actuator variance without shifting the operating point. In the presence of colored noise, long-range temporal correlations induce sampling-dependent deviations in both actuator mean and variance, defining the regime of validity of the memoryless Markov description. This framework provides a compact and physically transparent tool for analyzing and optimizing digitally stabilized
lasers in integrated photonic systems.
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Quantum Physics
Quantum target ranging with Hetero-Homodyne detection
Sangwoo Jeon, Yonggi Jo, Jihwan Kim et al. (+4 more)
Quantum target ranging, which estimates a target position using entangled
photon pairs, is known to offer an error-probability advantage over classical ranging strategies. Yet, realizing this advantage in practice remains challenging, as an existing receiver design relies on collective measurements and requires an impractically large number of
quantum memories and linear passive components. In this work, we propose the hetero-homodyne receiver, a practically implementable architecture that achieves
quantum advantage in target ranging using only local measurements. The receiver requires only one heterodyne setup, a single homodyne setup, and a delay line, making the implementation scalable and experimentally feasible. Our results establish a realistic framework for demonstrating
quantum advantage in target ranging and contribute toward practical
quantum radar systems.
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All authors Sangwoo Jeon, Yonggi Jo, Jihwan Kim, Zaeill Kim, Duk Y. Kim, Yong Sup Ihn, Su-Yong Lee
Quantum Physics
Linlin Ye, Zhaoqi Wu and Shao-Ming Fei
Shor's
algorithm outperforms its classical counterpart in efficient
prime factorization. We explore the coherence and
entanglement dynamics of the evolved states within Shor's
algorithm, showing that the coherence in each step relies on the dimension of register or the order, and discuss the relations between
geometric coherence and
geometric entanglement. We investigate how
unitary operators induce variations in coherence and
entanglement, and analyze the variations of coherence and
entanglement within the entire
algorithm, demonstrating that the overall effect of Shor's
algorithm tends to deplete coherence and produce
entanglement. Our research not only deepens the understanding of this
algorithm but also provides methodological references for studying resource dynamics in other
quantum algorithms.
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Quantum Physics
Enhanced Precision in Entangled Quantum Clocks with Phase Estimation Algorithm
Won-Young Hwang
We present an enhanced entangled-
quantum-clock protocol that incorporates a
quantum phase estimation
algorithm to directly estimate proper-time differences as an unknown phase. By employing highly entangled multi-clock states, the achievable uncertainty scales inversely with the total number of
quantum clocks, achieving the Heisenberg limit $O(1/N)$ while remaining completely immune to dynamical phase noise. Furthermore, we discuss the feasibility of utilizing this ultra-high precision protocol for gravitational wave detection, highlighting its potential for
quantum-enhanced relativistic sensing and fundamental physics tests.
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Quantum Physics
Quantifying magic via quantum $(\alpha,\beta)$ Jensen-Shannon divergence
Linmao Wang and Zhaoqi Wu
Magic states play an important role in fault-tolerant
quantum computation, and so the quantification of magic for
quantum states is of great significance. In this work, we propose two new magic quantifiers by introducing two versions of
quantum $(\alpha,\beta)$ Jensen-Shannon divergence based on the
quantum $(\alpha,\beta)$
entropy and the
quantum $(\alpha,\beta)$-relative
entropy, respectively. We derive many desirable properties for our magic quantifiers, and find that they are efficiently computable in low-dimensional
Hilbert spaces. We also show that the initial nonstabilizerness in the input state can boost the magic generating power for our magic quantifiers with appropriate parameter ranges for a certain class of
quantum gates. Our magic quantifiers may provide new tools for addressing some specific problems in magic resource theory.
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Quantum Physics
Deterministic linear-optical computing with symmetry-based qubits
David S. Simon, Christopher R. Schwarze, Anthony D. Manni et al. (+2 more)
A particular type of linear optical multiport, the Grover four-port, has previously been shown to couple the spatial
symmetry of a
photon to its direction of travel. It is shown here that use of a nonstandard choice of
qubit, based on
symmetry, allows Grover four ports to act as compact, low-resource deterministic linear optical controlledNOTgates, with no post-selection or ancilla measurements required. This approach allows programmable devices, made from Grover multiports in combination with other standard optical components, that can implement multiple different one-, two-, and three-
qubit gates, including the Fredkin and Toffoli gates.
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All authors David S. Simon, Christopher R. Schwarze, Anthony D. Manni, Abdoulaye Ndao, Alexander V. Sergienko
Quantum Physics
Database Reordering for Compact Grover Oracles with ESOP Minimization
Yusuke Kimura and Yutaka Takita
Grover's
algorithm searches for data satisfying a desired condition in an unstructured database. This
algorithm can search a space of size $N$ in $\sqrt{N}$ queries, thereby achieving a quadratic speedup. However, within the Grover oracle
circuit that is repeatedly applied, the
quantum state preparation
circuit – which embeds database information into
quantum states – suffers from a large gate count and
circuit depth. To address this problem, we propose reducing the
quantum state preparation
circuit by reordering the database. Specifically, we consider a
Quantum Read-Only
Memory (QROM), where data are assigned to addresses, and assume that the address assignment of data can be freely permuted. By applying Exclusive Sum-of-Products (ESOP) minimization to the resulting truth table, we reduce the
quantum circuit. Although the resulting
circuit logic differs from the original, the state preparation remains correct in the sense that every desired datum is encoded at some address. Furthermore, we propose a proxy metric that estimates
circuit size without compilation, and combine it with simulated annealing to efficiently find a near-optimal data ordering. In our experiments, an exhaustive search over all orderings for databases of size $N=8$ reveals that
circuit size varies by up to approximately a factor of two depending on the ordering, demonstrating the utility of reordering. Compared with applying ESOP minimization without reordering, simulated annealing reduces the
circuit size by approximately 30% and yields
circuits close to optimal. For $N=64$ and $128$, simulated annealing is shown to discover smaller
circuits compared with random search.
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Quantum Physics
Coherent feedback $H^\infty$ control of quantum linear systems
Guofeng Zhang and Ian R. Petersen
The purpose of this paper is to investigate the coherent feedback $H^\infty$ control problem for linear
quantum systems. A key contribution is a simplified design methodology that guarantees closed-loop stability and a prescribed level of disturbance attenuation. It is shown that for general linear
quantum systems, a physically realizable
quantum controller can be obtained by solving at most four Lyapunov equations. In the passive case, a necessary and sufficient condition is provided in terms of two uncoupled pairs of Lyapunov equations. These results represent a significant simplification over the standard approach, which requires solving two coupled algebraic Riccati equations. The effectiveness of the proposed method is demonstrated through two typical
quantum optical devices: an empty optical cavity and a degenerate parametric amplifier. These results provide a computationally efficient procedure for the robust and optimal control of
quantum optical and optomechanical systems.
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Quantum Physics
Discrete-variable assisted error correction of continuous-variable quantum information
Negin Razian, En-Jui Chang and Hoi-Kwan Lau
Robust continuous-variable (CV)
quantum information processing requires correcting realistic errors in bosonic systems, but all existing schemes rely on auxiliary Gottesman-Kitaev-Preskill (GKP) states which the preparation and operation are demanding in many platforms. In this work, we propose a novel CV
quantum error correction (QEC) scheme that utilizes a broadly accessible resource: discrete-variable (DV) ancilla. Our scheme extracts information about CV displacement to the DV ancilla, measuring that allows counteracting the unwanted displacement error. We show that a simple single-
qubit ancilla can already suppress CV infidelity by more than 20%. By concatenating with DV QEC codes, our scheme is robust against the physical errors in hybrid CV-DV systems, and yields a new class of oscillator-in-oscillator code that does not involve GKP states. Our work facilitates the implementation of CV QEC on realistic platforms.
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Quantum Physics · Cross-listed from hep-ph
Quantum-Inspired Tensor Network Autoencoders for Anomaly Detection: A MERA-Based Approach
Emre Gurkanli and Michael Spannowsky
We investigate whether a multiscale tensor-network architecture can provide a useful inductive bias for reconstruction-based anomaly detection in
collider jets. Jets are produced by a branching cascade, so their internal structure is naturally organised across angular and momentum scales. This motivates an autoencoder that compresses information hierarchically and can reorganise short-range correlations before coarse-graining. Guided by this picture, we formulate a MERA-inspired autoencoder acting directly on ordered jet constituents. To the best of our knowledge, a MERA-inspired autoencoder has not previously been proposed, and this architecture has not been explored in
collider anomaly detection. We compare this architecture to a dense autoencoder, the corresponding tree-tensor-network limit, and standard classical baselines within a common background-only reconstruction framework. The paper is organised around two main questions: whether locality-aware hierarchical compression is genuinely supported by the data, and whether the disentangling layers of MERA contribute beyond a simpler tree hierarchy. To address these questions, we combine
benchmark comparisons with a training-free local-compressibility diagnostic and a direct identity-disentangler ablation. The resulting picture is that the locality-preserving multiscale structure is well matched to jet data, and that the MERA disentanglers become beneficial precisely when the compression bottleneck is strongest. Overall, the study supports locality-aware hierarchical compression as a useful inductive bias for jet anomaly detection.
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