Quantum Physics · Cross-listed from cond-mat.mes-hall
Fast high-fidelity baseband reset of a latched state for quantum dot qubit readout
Piotr Marciniec, M. A. Wolfe, Tyler Kovach et al. (+9 more)
A common method for reading out the state of a
spin qubit is by latching one logical
qubit state, either $|1\rangle$ or $|0\rangle$, onto a different, metastable charge state. Such a latched state can provide a superior charge sensing signal for
qubit readout, and it can have a lifetime chosen to be long enough that the charge sensed readout can be high fidelity. However, the passive reset out of latched states is inherently long, which is not desirable. In this work, we demonstrate an on-demand, high fidelity (> 99%) re-initialization of a
quantum dot
qubit out of a latched readout state. The method is simple to apply as it involves a single baseband voltage pulse to a specific region in the
quantum dot stability diagram where the relaxation time from the latched state to the ground state is over 50 times faster. We describe the mechanism for the reset process as well as the boundaries for the optimal reset region in the
qubit gate voltage space.
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All authors Piotr Marciniec, M. A. Wolfe, Tyler Kovach, J. Reily, Sanghyeok Park, Jared Benson, Mark Friesen, Benjamin D. Woods, Matthew J. Curry, Nathaniel C. Bishop, J. Corrigan, M. A. Eriksson
Quantum Physics · Cross-listed from hep-th
Conformal Blocks in 2d Carrollian/Galilean CFTs and Excited State Entanglement Entropy
Peng-Xiang Hao and Shunta Takahashi
We advance the study of flat space holography by computing the
entanglement entropy of highly excited states in two-dimensional Carrollian/Galilean Conformal Field Theories (C/G CFTs). Our approach is centered on a novel, physically intuitive derivation of the heavy-light conformal block in the large central charge limit, where the backreaction of heavy operators is absorbed by a C/G conformal coordinate transformation. Using this result and the replica trick, we find that the
entanglement entropy of highly excited states assumes a thermal form, providing a concrete realization of the Eigenstate Thermalization Hypothesis (ETH). This field-theoretic result perfectly reproduces the
holographic entanglement entropy computed via the swing surface proposal in three-dimensional Einstein
gravity, for backgrounds corresponding to spinning particles and Flat Space Cosmological solutions. This agreement establishes a precise dictionary relating the weight $\Delta$ and charge $\xi$ of the boundary state to the mass $m$ and angular momentum $j$ of the dual spacetime, offering a powerful consistency check for the Flat/CCFT correspondence.
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Quantum Physics
Quantum simulation of actinide chemistry: towards scalable algorithms on trapped ion quantum computers
Kesha Sorathia, Cono Di Paola, Gabriel Greene-Diniz et al. (+9 more)
Due to the wide range of technical applications of actinide elements, a thorough understanding of their electronic structure could complement technological improvements in many different areas.
Quantum computing could greatly aid in this understanding, as it can potentially provide exponential speedups over classical approaches, thereby offering insights into the complex electronic structure of actinide compounds. As a first foray into
quantum computational chemistry of actinides, this paper compares the method of
quantum computed moments (QCM) as a noisy intermediate-scale
quantum algorithm with a single-ancilla version of
quantum phase estimation (QPE), a
quantum algorithm expected to run on fault-tolerant
quantum computers. We employ these
algorithms to study the reaction energetics of plutonium
oxides and hydrides. In order to enable
quantum hardware experiments, we use several techniques to reduce resource requirements: screening individual
Hamiltonian Pauli terms to reduce the measurement requirements of QCM and variational compilation to reduce the depth of QPE
circuits. Finally, we derive electronic structure descriptions from a series of representative chemical models and compute the energetics from
quantum experiments on Quantinuum's H-series ion trap devices using up to 19
qubits. We find our experiments to be in excellent agreement with results from classical electronic structure calculations and state vector simulations.
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All authors Kesha Sorathia, Cono Di Paola, Gabriel Greene-Diniz, Carlo A. Gaggioli, David Zsolt Manrique, Joe Gibbs, Sean Harding, Thomas M. Soini, Neil Gaspar, Robert Harker, Mark Storr, David Munoz Ramo
Quantum Physics
Accurate Leakage Speculation for Quantum Error Correction
Chaithanya Naik Mude and Swamit Tannu
Quantum Error Correction (QEC) protects
qubits against bit- and phase-flip errors in the |0> or |1> subspace, but physical
qubits can also leak into higher energy levels (e.g., |2>). Leakage is especially harmful, as it corrupts all subsequent syndrome measurements and can spread to neighboring
qubits. Detecting leakage on data
qubits is particularly challenging, since they are never measured directly during QEC cycles. Prior work, such as eraser, addresses this by inferring leakage from syndrome patterns using a fixed heuristic. However, this approach often misclassifies benign syndromes, triggering excessive leakage-reduction
circuits (LRCs). Because LRCs are themselves noisy and slow, these false triggers lengthen QEC cycles and inflate logical error rates. We propose gladiator, a general and adaptable leakage speculation framework that works across surface code, color code, and qLDPC codes. Offline, gladiator builds a code-aware error-propagation graph calibrated to device data. Online, it classifies each syndrome in a few nanoseconds and schedules LRC only when the observed pattern is provably leakage-dominated. This precise speculation eliminates up to 3x (and on average 2x) unnecessary LRCs, shortens QEC cycles, and suppresses false positives at their source. Evaluated on standard fault-tolerant
benchmarks, gladiator delivers 1.7x-3.9x speedups and 16% reduction in logical error rate, advancing the efficiency of fault-tolerant
quantum computing.
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Quantum Physics
Large-scale implementation of quantum subspace expansion with classical shadows
Laurin E. Fischer, Daniel Bultrini, Ivano Tavernelli et al. (+1 more)
Quantum subspace expansion (QSE) offers promising avenues to perform spectral calculations on
quantum processors but comes with a large measurement overhead. Informationally complete (IC) measurements, such as classical shadows, were recently proposed to overcome this bottleneck. Here, we report the first large-scale implementation of QSE with IC measurements. In particular, we probe the
quantum phase transition of a
spin model with three-body interactions, for which we observe accurate ground state energy recovery and mitigation of local order parameters across system sizes of up to 80
qubits. We achieve this by reformulating QSE as a constrained optimization problem, obtaining rigorous statistical error estimates and avoiding numerical ill-conditioning. With over $3 \times 10^4$ measurement basis randomizations per
circuit and the evaluation of $O(10^{14})$ Pauli traces, this represents one of the most significant experimental realizations of classical shadows to date.
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All authors Laurin E. Fischer, Daniel Bultrini, Ivano Tavernelli, Francesco Tacchino
Quantum Physics
Photoelectric detection of single spins in diamond by optically controlled discharge of long-lived trap states
A. C. Ulibarri, D. J. McCloskey, D. Wang et al. (+3 more)
Electrical detection methods for solid-state
spins are attractive for
quantum technologies, being readily chip-scalable and not subject to the small
photon budgets of single emitters. However, realising electrical
spin readout in wide-bandgap materials with similar fidelity and bandwidth to optical approaches remains challenging. Here, we introduce a photoelectrical
spin readout scheme that detects
spin information stored long-term as trapped electrical charges. Using nitrogen-vacancy (NV) centres in diamond as a model system,
spin-dependent photoionisation generates charge carriers that are stored in long-lived trap states at a diamond-metal Schottky junction. On-demand illumination of the junction under electrical bias releases stored charge, yielding a photocurrent transient proportional to the amount of trapped charge and hence
spin state.
Spin readout after coherent control of single NVs is demonstrated using charge readout in a protocol we call charge-capture detected
magnetic resonance (CCDMR), and we use charge-based imaging to identify charge carrier generation and trapping processes. Our results establish CCDMR as a new technique for solid-state
spin qubit readout, combining attaractive features of electrical detection with the stability of long-lived charge traps in wide-bandgap materials.
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All authors A. C. Ulibarri, D. J. McCloskey, D. Wang, N. Dontschuk, A. M. Martin, A. A. Wood
Quantum Physics
Engineering Atom-Photon Hybridization with Density-Modulated Atomic Ensembles in Coupled Cavities
Carlos E. Máximo, Romain Bachelard and Tobias Donner
Radiation-matter hybridization allows atoms to serve as mediators of effective interactions between light modes and, conversely, to interact among themselves via light. Here we exploit the spatial structure of atomic ensembles to control the coupling between modes of distinct cavities, thereby reshaping the resulting atom-
photon spectra. We show that extended homogeneous clouds suppress mode-mode couplings through destructive interference, whereas grated clouds can preserve them under specific Bragg conditions. This leads to mode-mode spectral subsplittings, where collectivity arises not only from the atom number but also from the ability to tune modes of different cavities independently. Our results establish spatially engineered atomic ensembles as a pathway to selective
photon transfer between modes and precise control of many-body complexity.
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Quantum Physics
Controlling the Dynamical Evolution of Quantum Coherence and Quantum Correlations in $ e^{+}e^{-} \to \Lambda\bar{\Lambda}$ Processes at BESIII
Elhabib Jaloum and Mohamed Amazioug
Quantum coherence, a cornerstone of
quantum mechanics, is of paramount importance for
quantum information protocols. However, maintaining coherence in elementary particle systems presents significant challenges. In this work, we investigate
quantum coherence and
quantum correlations in the $e^{+}e^{-} \to \Lambda\bar{\Lambda}$ processes at BESIII using experimentally feasible parameters, where $\Lambda$ and $\bar{\Lambda}$ denote the
spin-$1/2$ hyperon and its antihyperon, respectively. We analyze the dependence of
quantum coherence and
quantum correlations on the scattering angle $\varphi$. Notably, these resources reach their maximum at $\varphi=\pi/2$. We demonstrate that classical correlations can significantly delay the decay of
quantum correlations and coherence. This study underscores the importance of understanding the interplay between classical and
quantum correlations in high-energy particle physics, particularly in the context of hyperon-antihyperon interactions explored in the BESIII experiment. This result could have potential applications in
quantum information processing and high-energy physics.
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Quantum Physics
Systematic Non-Binary Extension of LDPC-CSS Codes Preserving Orthogonality
Kenta Kasai
We study finite-field extensions that preserve the same support as the parity-check
matrices defining a given binary CSS code. Here, an LDPC-CSS code refers to a CSS code whose parity-check
matrices are orthogonal in the sense that each pair of corresponding rows overlaps in an even (possibly zero) number of positions, typically at most twice in sparse constructions. Beyond the low-density setting, we further propose a systematic construction method that extends to arbitrary CSS codes, providing feasible finite-field generalizations that maintain both the binary support and the orthogonality condition.
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Quantum Physics
Transition-aware decomposition of single-qudit gates
Denis A. Drozhzhin, Evgeniy O. Kiktenko, Aleksey K. Fedorov et al. (+1 more)
Quantum computation with $d$-level
quantum systems, also known as qudits, benefits from the possibility to use a richer computational space compared to
qubits. However, for an arbitrary qudit-based hardware platform, the issue is that a generic qudit operation has to be decomposed into the sequence of native operations $-$ pulses that are adjusted to the transitions between two levels in a qudit. Typically, not all levels in a qudit are simply connected to each other due to specific selection rules. Moreover, the number of pulses plays a significant role, since each pulse takes a certain execution time and may introduce error. In this paper, we propose a resource-efficient
algorithm to decompose single-qudit operations into the sequence of pulses that are allowed by qudit selection rules. Using the developed
algorithm, the number of pulses is at most $d(d{-}1)/2$ for an arbitrary single-qudit operation. For specific operations, the
algorithm could produce even fewer pulses. We provide a comparison of qudit decompositions for several types of trapped ions, specifically $^{171}\text{Yb}^+$, $^{137}\text{Ba}^+$ and $^{40}\text{Ca}^+$ with different selection rules, and also decomposition for superconducting qudits. Although our approach deals with single-qudit operations, the proposed approach is important for realizing two-qudit operations since they can be implemented as a standard two-
qubit gate that is surrounded by efficiently implemented single-qudit gates.
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All authors Denis A. Drozhzhin, Evgeniy O. Kiktenko, Aleksey K. Fedorov, Anastasiia S. Nikolaeva
Quantum Physics · Cross-listed from cs.LG
Hybrid Quantum-Classical Recurrent Neural Networks
Wenduan Xu
We present a hybrid
quantum-classical recurrent neural network (QRNN) architecture in which the recurrent core is realized as a parametrized
quantum circuit (PQC) controlled by a classical feedforward network. The hidden state is the
quantum state of an $n$-
qubit PQC in an exponentially large
Hilbert space $\mathbb{C}^{2^n}$, which serves as a coherent recurrent
quantum memory. The PQC is
unitary by construction, making the hidden-state
evolution norm-preserving without external constraints. At each timestep, mid-
circuit Pauli expectation-value readouts are combined with the input
embedding and processed by the feedforward network, which provides explicit classical nonlinearity. The outputs parametrize the PQC, which updates the hidden state via
unitary dynamics. The QRNN is compact and physically consistent, and it unifies (i)
unitary recurrence as a high-capacity
memory, (ii) partial observation via mid-
circuit readouts, and (iii) nonlinear classical control for input-conditioned parametrization. We evaluate the model in simulation with up to 14
qubits on sentiment analysis, MNIST, permuted MNIST, copying
memory, and
language modeling. For sequence-to-sequence learning, we further devise a soft
attention mechanism over the mid-
circuit readouts and show its effectiveness for machine translation. To our knowledge, this is the first model (RNN or otherwise) grounded in
quantum operations to achieve competitive performance against strong classical baselines across a broad class of sequence-learning tasks.
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Quantum Physics
Charge-Preserving Operations in Quantum Batteries
André H. A. Malavazi, Borhan Ahmadi, Paweł Horodecki et al. (+1 more)
Ergotropy provides a fundamental measure of the extractable work from a
quantum system and, consequently, of the maximal useful energy, or charge, stored within it. Understanding how this quantity can be manipulated and transformed efficiently is crucial for advancing
quantum energy management technologies. Here, we introduce and formalize the concepts of isoergotropic states and ergotropy-preserving operations, which reorganize the internal structure of ergotropy while keeping its total value unchanged. These ideas are illustrated for both discrete (two-level systems) and continuous-variable systems (single-mode Gaussian states). In each case, we show how ergotropy-preserving operations redistribute the respective coherent-incoherent and displacement-squeezing components. We further examine the thermodynamic exchanges accompanying ergotropy-preserving operations, including variations in energy and
entropy, and demonstrate that these transformations can be dynamically implemented through standard beam-splitter-type interactions with an auxiliary system. Finally, we discuss the practical implications of isoergotropic states and operations in optimizing charging protocols and mitigating charge loss in open
quantum batteries.
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All authors André H. A. Malavazi, Borhan Ahmadi, Paweł Horodecki, Pedro R. Dieguez
Quantum Physics
Model Reduction for Controlled Quantum Markov Dynamics
Tommaso Grigoletto, Lorenza Viola and Francesco Ticozzi
We consider the problem of model reduction for Markovian
quantum systems whose dynamics are described by a time-dependent Lindblad generator – notably, as arising in the presence of external control. Our approach, which builds upon Krylov operator subspaces and operator-algebraic techniques introduced for time-independent generators, returns a reduced model that reproduces exactly the
evolution of observables of interest and is guaranteed to be in Lindblad form.
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Quantum Physics
Super-Moiré Spin Textures in Twisted Antiferromagnets
King Cho Wong, Ruoming Peng, Eric Anderson et al. (+15 more)
Stacking two-dimensional (2D) layered materials offers a powerful platform to engineer electronic and
magnetic states. In general, the resulting states, such as Moiré magnetism, have a periodicity at the length scale of the Moiré unit
cell. Here, we report a new type of magnetism – dubbed a super-Moiré
magnetic state – which is characterized by long-range
magnetic textures extending beyond the single Moiré unit
cell – in twisted double
bilayer chromium triiodide (tDB CrI$_3$). We found that at small twist angles, the size of the spontaneous
magnetic texture increases with twist angle, opposite to the underlying Moiré periodicity. The
spin-texture size reaches a maximum of about 300 nm in 1.1${\deg}$ twisted devices, an order of magnitude larger than the underlying Moiré wavelength, and vanishes at twist angles above 2${\deg}$. Employing scanning
quantum spin magnetometry, the obtained vector field maps suggest the formation of
antiferromagnetic Néel-type skyrmions spanning multiple Moiré
cells. The twist-angle-dependent study combined with large-scale atomistic simulations suggests that complex
magnetic competition between the Dzyaloshinskii–Moriya interaction,
magnetic anisotropy, and exchange interactions controlled by the relative rotation of the layers produces the topological textures which arise in the super-Moiré
spin orders.
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All authors King Cho Wong, Ruoming Peng, Eric Anderson, Jackson Ross, Bowen Yang, Meixin Cheng, Sreehari Jayaram, Malik Lenger, Xuankai Zhou, Yan Tung Kong, Takashi Taniguchi, Kenji Watanabe, Michael A. McGuire, Rainer Stöhr, Adam Wei Tsen, Elton J. G. Santos, Xiaodong Xu, Jörg Wrachtrup
Quantum Physics
Second-order Stark shifts exceeding 10$\,$GHz in electrically contacted SiV$^-$ centers in diamond
Manuel Rieger, Nori N. Chavira Leal, Rubek Poudel et al. (+7 more)
Negatively charged silicon vacancy centers (SiV$^-$) in diamond exhibit excellent
spin coherence and optical properties, making them promising candidates for
quantum technologies. However, the strain-induced inhomogeneous distribution of optical transition frequencies poses a challenge for scalability. We demonstrate electrical tuning of the SiV$^-$ center zero-
phonon lines using in-plane contacts to apply moderate electric fields up to 45$\,$MV/m. The second-order Stark shift exceeds 10$\,$GHz, which is of the same order of magnitude as the 15$\,$GHz inhomogeneous distribution of SiV$^-$ observed in emitters embedded in optical nanostructures such as photonic
crystal nanocavities. Analysis of individual SiV$^-$ centers shows significant variation in polarizabilities between defects indicating that the polarizability strongly depends on local parameters like strain. The observed polarizabilities are 3-25 times larger than those of tin vacancy centers, which we attribute to valence band resonances that delocalize the $e_u$ wavefunctions. Photoluminescence excitation measurements reveal that optical linewidths increase moderately with applied electric field strength. Our results demonstrate that large electrical Stark shifts can overcome the inhomogeneous distribution of transition frequencies, representing a significant step toward scalable SiV$^-$-based
quantum technologies such as
quantum repeaters.
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All authors Manuel Rieger, Nori N. Chavira Leal, Rubek Poudel, Tobias Waldmann, Lina M. Todenhagen, Stefan Kresta, Viviana Villafane, Martin S. Brandt, Kai Müller, Jonathan J. Finley
Quantum Physics · Cross-listed from physics.optics
Next-generation interferometry with gauge-invariant linear optical scatterers
Christopher R. Schwarze, Anthony D. Manni, David S. Simon et al. (+2 more)
Measurement technology employing optical interference phenomena such as a fringe pattern or frequency shift has been evolving for more than a century. The systems are being designed better, and their components are being built better. But the major components themselves hardly change. Most modern interferometers rely on the same conventional set of components to separate the electromagnetic field into multiple beams, such as plate optics and beam-splitters. This naturally limits the design scope and thus the potential applicability and performance. However, recent investigations suggest that incorporating novel, higher-dimensional linear-optical splitters in interferometer design can lead to several improvements. In this work, we review the underlying theory of these novel optical scatterers and some demonstrated configurations with enhanced resolution. The basic principles of optical interference and optical phase sensing are discussed in tandem. Emphasis is placed on both familiar and unfamiliar scatterers, such as the maximally-symmetric Grover multiport, whose actions are left unchanged by certain gauge transformations. These higher-dimensional, gauge-invariant multiports embody a new class of building blocks which can tailor optical interference for metrology in unconventional ways.
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All authors Christopher R. Schwarze, Anthony D. Manni, David S. Simon, Abdoulaye Ndao, Alexander V. Sergienko
Quantum Physics · Cross-listed from cond-mat.stat-mech
Dynamics of entanglement fluctuations and quantum Mpemba effect in the $\nu=1$ QSSEP model
Angelo Russotto, Filiberto Ares, Pasquale Calabrese et al. (+1 more)
We study the out-of-
equilibrium dynamics of
entanglement fluctuations in the $\nu=1$
Quantum Symmetric Simple Exclusion Process, a free-
fermion chain with hopping amplitudes that are
stochastic in time but homogeneous in space. Previous work showed that the average
entanglement growth after a
quantum quench can be explained in terms of pairs of entangled quasiparticles performing random walks, leading to diffusive
entanglement spreading. By incorporating the noise-induced statistical correlations between the quasiparticles, we extend this description to the full-time probability distribution of the
entanglement entropy. Our generalized quasiparticle picture allows us to compute the average time
evolution of a generic function of the reduced density
matrix of a subsystem. We also apply our result to the
entanglement asymmetry. This allows us to investigate the restoration of particle-number
symmetry in the dynamics from initial states with no well-defined particle number. Regarding the possible existence of the
quantum Mpemba effect, our analysis indicates that its occurrence is an extremely fine-tuned phenomenon, requiring very specific conditions and therefore being rather difficult to observe in practice.
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All authors Angelo Russotto, Filiberto Ares, Pasquale Calabrese, Vincenzo Alba
Quantum Physics
Decoherence Estimation of Superconducting Qubit
Yoav Koral, Shilo Avraham, Manimuthu Peryasamy et al. (+2 more)
Decoherence of
quantum bits arises primarily from the parasitic resistance within the
qubit. This study presents the analysis of the decoherence process due to physical interactions between the
qubit photons and parasitic resistance atoms, utilizing exclusively the Caldeira-Leggett electrical model, without relying on external
Hamiltonians. The analysis shows a good agreement between the model of the electrical noise and the Johnson-Nyquist noise. The emission and absorption rates of the
qubit's coherent loss, required for the Lindblad master equation that approximates the decoherence, are obtained. A numerical substitution in the analysis result yields a strong correlation with previous measurements. The present analysis enables also the derivation of the appropriate
circuit characteristics for future simulations.
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All authors Yoav Koral, Shilo Avraham, Manimuthu Peryasamy, Shmuel E. Schacham, Eliyahu Farber
Quantum Physics · Cross-listed from math.PR
On the injective norm of random fermionic states and skew-symmetric tensors
Stephane Dartois and Parham Radpay
We study the injective norm of random skew-symmetric tensors and the associated fermionic
quantum states, a natural measure of multipartite
entanglement for systems of indistinguishable particles. Extending recent advances on random
quantum states, we analyze both real and complex skew-symmetric Gaussian ensembles in two asymptotic regimes: fixed particle number with increasing one-particle
Hilbert space dimension, and joint scaling with fixed filling fraction. Using the Kac–Rice formula on the Grassmann
manifold, we derive high-probability upper bounds on the injective norm and establish sharp asymptotics in both regimes. Interestingly, a duality relation under particle–hole transformation is uncovered, revealing a
symmetry of the injective norm under the action of the Hodge
star operator. We complement our analytical results with numerical simulations for low
fermion numbers, which match the predicted bounds.
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Quantum Physics
Detuning Choice for solving MIS and MWIS
Sem Saada Khelkhal and Louis Barcikowsky
We address the realization of Maximum Weighted Independent Set (MWIS) and
quantum Maximum Independent Set (MIS) problems under Pasqal's neutral-atom QPU constraints: limited
qubit number, bounds on {\Omega} and {\Delta}, sequence duration, confinement space, minimum distances, and parasitic interactions. To obtain results directly compatible with current hardware, we propose a new detuning computation method that mitigates parasitic interactions in arbitrary asymmetric graphs. Three variants are introduced, matching different hardware maturity levels: (I) a theoretical local-detuning approach; (II) a Detuning Map Modulation (DMM) method bridging theory and near-term feasibility; and (III) a global-pulse implementation suitable for current QPUs. All were evaluated on Pasqal's emulators for graphs up to 30
qubits, demonstrating realistic, transferable performance within present-day hardware limits.
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Quantum Physics
Generalized collective quantum tomography: algorithm design, optimization, and validation
Shuixin Xiao, Yuanlong Wang, Zhibo Hou et al. (+6 more)
Quantum tomography is a fundamental technique for characterizing, benchmarking, and verifying
quantum states and devices. It plays a crucial role in advancing
quantum technologies and deepening our understanding of
quantum mechanics. Collective
quantum state
tomography, which estimates an unknown state h̊o} through joint measurements on multiple copies $\rho\otimes\cdots\otimes\rho$ of the unknown state, offers superior information extraction efficiency. Here we extend this framework to a generalized setting where the target becomes $S_1\otimes\cdots\otimes S_n$, with each $S_i$ representing identical or distinct
quantum states, detectors, or processes from the same category. We formulate these tasks as optimization problems and develop three
algorithms for collective
quantum state, detector and process
tomography, respectively, each accompanied by an analytical characterization of the computational complexity and mean squared error (MSE) scaling. Furthermore, we develop optimal solutions of these optimization problems using sum of squares (SOS) techniques with semi-algebraic constraints. The effectiveness of our proposed methods is demonstrated through numerical examples. Additionally, we experimentally demonstrate the
algorithms using two-copy collective measurements, where entangled measurements directly provide information about the state purity. Compared to existing methods, our
algorithms achieve lower MSEs and approach the collective MSE bound by effectively leveraging purity information.
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All authors Shuixin Xiao, Yuanlong Wang, Zhibo Hou, Aritra Das, Ian R. Petersen, Farhad Farokhi, Guo-Yong Xiang, Jie Zhao, Daoyi Dong
Quantum Physics
Quantum Fisher Information With General Quantum Coherence in multi-dimensional quantum systems
Jun-Long Zhao, Li Yu, Ming Yang et al. (+1 more)
Quantum metrology is a science about
quantum measurements and it plays a key role in precision of
quantum parameter estimation. Meanwhile,
quantum coherence is an important
quantum feature and
quantum Fisher information (QFI) is an important indicator for precision of
quantum parameter estimation. In this paper, we explore the relationship between QFI and
quantum coherence in multi-dimensional
quantum systems. We introduce a new concept referred to as General
Quantum Coherence (GQC), which characterizes the
quantum coherence and the eigenenergies of the
Hamiltonian in the interaction processes. GQC captures
quantum nature of high-dimensional
quantum states and addresses shortcomings in coherence measurement. Additionally, we observe a stringent square relationship between GQC and QFI. This finding provides a crucial guideline for improving the precision of parameter estimation.
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All authors Jun-Long Zhao, Li Yu, Ming Yang, Chui-Ping Yang
Quantum Physics
Variational quantum computing for quantum simulation: principles, implementations, and challenges
Lucas Q. Galvão, Anna Beatriz M. de Souza, Marcelo A. Moret et al. (+1 more)
This work presents a comprehensive overview of variational
quantum computing and their key role in advancing
quantum simulation. This work explores the simulation of
quantum systems and sets itself apart from approaches centered on classical data processing, by focusing on the critical role of
quantum data in Variational
Quantum Algorithms (VQA) and
Quantum Machine Learning (QML). We systematically delineate the foundational principles of variational
quantum computing, establish their motivational and challenges context within the noisy intermediate-scale
quantum (NISQ) era, and critically examine their application across a range of prototypical
quantum simulation problems. Operating within a hybrid
quantum-classical framework, these
algorithms represent a promising yet problem-dependent pathway whose practicality remains contingent on trainability and scalability under noise and barren-plateau constraints.This review serves to complement and extend existing literature by synthesizing the most recent advancements in the field and providing a focused perspective on the persistent challenges and emerging opportunities that define the current landscape of variational
quantum computing for
quantum simulation.
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All authors Lucas Q. Galvão, Anna Beatriz M. de Souza, Marcelo A. Moret, Clebson Cruz
Quantum Physics · Cross-listed from hep-th
Groupoid Representation of Lorentz Transformations Including Superluminal Observers
Marco Zaopo
We construct a Minkowski-pointed Poincare groupoid that extends the
geometric description of Lorentz transformations to frames superluminal relative to a distinguished rest frame. Real four-dimensional superluminal boost
matrices factorize into ordinary Lorentz boosts and finite infinite-speed limits. For each spatial direction, the two oriented limits define arrows between the Minkowski metric object and a directional metric object; their composition yields an involutive isotropy loop generating a direction-dependent extension of the Poincare group. These arrows induce *-isomorphisms of Poincare observable
algebras, transporting generators and their tensor products. Since all metric objects share a common affine spacetime and dual momentum space, transported spectral data can be classified relative to the distinguished Minkowski metric. This Minkowski-pointed classification recovers ordinary massive and massless Wigner sectors and assigns spacelike orbits, with SO(2,1) little groups, to massive momentum representatives transported to directional objects. It thus provides a
geometric interpretation of tachyonic Wigner wavefunction classes without postulating intrinsically tachyonic states. As a kinematic application, we examine polarized cobalt-60 beta decay. Under an explicit source-arrow correspondence, reversal of
nuclear polarization exchanges oriented arrows and reverses the preferred momentum direction, consistently with the observed reversal of the Wu counting asymmetry. The measured angular law is compatible with this correspondence; a derivation of decay amplitudes and asymmetry coefficients remains open.
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Quantum Physics · Cross-listed from cond-mat.str-el
Immobile and mobile excitations of three-spin interactions on the diamond chain
M. Bayer, M. Vieweg and K.P. Schmidt
We present a solvable one-dimensional
spin-1/2 model on the diamond chain featuring three-
spin interactions, which displays both, mobile excitations driving a second-order phase transition between an ordered and a $\mathbb{Z}_2$-
symmetry broken phase, as well as non-trivial fully immobile excitations. The model is motivated by the physics of fracton excitations, which only possess mobility in a reduced dimension compared to the full model. We provide an exact mapping of this model to an arbitrary number of independent transverse-field Ising chain segments with open boundary conditions. The number and lengths of these segments correspond directly to the number of immobile excitations and their respective distances from one another. Furthermore, we demonstrate that multiple immobile excitations exhibit Casimir-like forces between them, resulting in a non-trivial spectrum.
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Quantum Physics
Quantum-correlated photons from spectrally-separated modes of a cavity coupled to a strongly-driven two-level atom
Alex Elliott, Jacob Ngaha, Scott Parkins et al. (+1 more)
Photon counting statistics are explored, theoretically, from a pair of cavity modes coupled to the fluorescent transitions in a strongly-driven two-level atom. We show that the cavity modes acquire nonclassical
photon statistics that are representative of dressed-state picture atomic transitions. In particular, the modes are shown to be antibunched, while simultaneously having a cross-correlation value greater than unity. Furthermore, we propose an implementation of the system with a nanofiber cavity QED system, based on a strongly-driven cesium atom.
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All authors Alex Elliott, Jacob Ngaha, Scott Parkins, Takao Aoki
Quantum Physics
Imaginarity measures induced by real part states and the complementarity relations
Jingyan Liu, Yue Sun, Jianwei Xu et al. (+1 more)
Complex numbers are indispensable in
quantum mechanics and the resource theory of imaginarity has been developed recently. In this paper, we propose a method to construct imaginary measures by real part states. Specifically, we propose an imaginarity measure in terms of fidelity and explore its properties. The analytical expression of the imaginarity measure is presented in
qubit systems. The relations between the proposed imaginarity measure and some other imaginarity measures (such as
geometric imaginarity, Tsallis relative
entropy imaginarity and trace norm imaginarity) are derived. The complementarity relations of the imaginarity measure under a complete set of mutually unbiased bases are provided in low-dimensional systems. This work not only highlights the prominent role of the real part state in the imaginarity resource theory, but also reveals the constraint of imaginarity on a complete set of mutually unbiased bases physically.
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All authors Jingyan Liu, Yue Sun, Jianwei Xu, Ming-Jing Zhao
Quantum Physics
Design and Fabrication of Metal-Shielded Fiber-Cavity Mirrors for Ion-Trap Systems
Wei-Bin Chen, Ding Fang, Cheng-Hao Zhang et al. (+4 more)
Trapped ions in micro-cavities constitute a key platform for advancing
quantum information processing and
quantum networking. By providing an efficient light-matter interface within a compact architecture, they serve as highly efficient
quantum nodes with strong potential for scalable
quantum network. However, in such systems, ion trapping stability is often compromised by surface charging effects, and nearby dielectric materials are known to cause a dramatic increase in the ion heating rate by several orders of magnitude. These challenges significantly hinder the practical implementation of ion trap systems integrated with micro-cavities. To overcome these limitations, we present the design and fabrication of metal-shielded micro-cavity mirrors, enabling the stable realization of ion trap systems integrated with micro cavities. Using this method, we constructed a needle ion trap integrated with fiber Fabry-Perot cavity and successfully achieved stable trapping of a single ion within the cavity. The measured ion heating rate was reduced by more than an order of magnitude compared with unshielded configurations. This work establishes a key technique toward fully integrated ion-
photon interfaces for scalable
quantum network.
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All authors Wei-Bin Chen, Ding Fang, Cheng-Hao Zhang, Jin-Ming Cui, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo
Quantum Physics
Statistical mechanics from quantum envariance and exchange symmetry
Amul Ojha, Shubhit Sardana and Arnab Ghosh
We build on the foundational work of Deffner and Zurek [S. Deffner and W. H. Zurek, New J. Phys. 18, 063013 (2016)] to show how central
equilibrium structures of statistical mechanics can be understood within standard
quantum mechanics using the concept of envariance (environment-assisted invariance). In particular, we show how the Binomial, Poisson, and Gaussian distributions naturally emerge from entangled system-environment states. We revisit the Gibbs paradox from a
quantum information perspective, demonstrating that the standard Sackur-Tetrode
entropy and its 1/N! factor arise from indistinguishability enforced through
entanglement with an environment, without introducing additional thermodynamic corrections. Within the same framework, we analyze ionization
equilibrium and show how the classical Saha equation is recovered, while clarifying how indistinguishability enters through an
entanglement-induced reduction of permutation redundancy. Assuming the standard exchange
symmetries of identical
quantum particles, we further show how the Bose-Einstein and
Fermi-Dirac distributions follow as the
equilibrium weighting of
symmetry-allowed occupation configurations. Overall, our results support the view that
equilibrium statistical mechanics can be consistently interpreted as an emergent consequence of
quantum information-theoretic structure and
symmetry, rather than as a collection of independent phenomenological postulates.
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Quantum Physics
Encoding computationally hard problems in triangular Rydberg atom arrays
Xi-Wei Pan, Huan-Hai Zhou, Yi-Ming Lu et al. (+1 more)
Rydberg atom arrays are a promising platform for
quantum optimization, encoding computationally hard problems by reducing them to independent set problems with unit-disk graph
topology. In Nguyen et al., PRX
Quantum 4, 010316 (2023), a systematic and efficient strategy was introduced to encode multiple problems into a special unit-disk graph: the King's subgraph. However, King's subgraphs are not the optimal choice in two dimensions. Due to the power-law decay of Rydberg interaction strengths, the approximation to unit-disk graphs in real devices is poor, necessitating post-processing that lacks physical interpretability. In this work, we develop an encoding scheme that can universally encode computationally hard problems on triangular
lattices, based on our innovative automated gadget search strategy. Numerical simulations demonstrate that
quantum optimization on triangular
lattices reduces independence-constraint violations by approximately two orders of magnitude compared to King's subgraphs, substantially alleviating the need for post-processing in experiments.
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All authors Xi-Wei Pan, Huan-Hai Zhou, Yi-Ming Lu, Jin-Guo Liu