Quantum Physics · Cross-listed from physics.bio-ph
Magnetosensitivity of amphibian morphological pigmentation is light- and eye-dependent and consistent with the radical pair mechanism
Hadi Zadeh-Haghighi, Gabriel E. Bertolesi, Sarah McFarlane et al. (+1 more)
Weak
magnetic fields influence a wide range of biological processes, yet the underlying mechanisms are poorly understood. The radical pair mechanism (RPM), which involves
quantum spin dynamics, is a leading hypothesis. Here we show that weak
magnetic fields modulate morphological pigmentation – specifically, the number of perioptic melanophores – in Xenopus laevis tadpoles in a field-strength-dependent manner. The response is light- and eye-dependent. The observed field-strength dependence is quantitatively consistent with a radical pair model. These properties are reminiscent of the light-dependent magnetoreception that is thought to operate in migratory birds, and establish amphibian pigmentation as a tractable vertebrate system for the study of radical-pair
quantum biology.
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All authors Hadi Zadeh-Haghighi, Gabriel E. Bertolesi, Sarah McFarlane, Christoph Simon
Quantum Physics
The verifier side of speculative window decoding: a predictability bracket, a machine-checked blast-radius bound, and a decoder-agnostic recover loop
Rylan Malarchick
Speculative window decoders hide
quantum error-correction decoder latency by guessing the cross-boundary decisions that link adjacent decoding windows, running downstream work on the guess, and verifying lazily. SWIPER and ARTERY each build one predictor, about 90% accurate; neither built the verifier side. We build it on a reconstructed SWIPER harness (Stim rotated surface code, minimum-weight matching). A predictor-only bracket shows the cross-boundary decision is local, the achievable accuracy reaching about 0.999 within three rounds, with small, diffuse headroom over SWIPER. We establish a worst-case temporal blast-radius bound, its probability core machine-checked in Lean4 and conditional on a modeling reduction we then test: a misprediction's effect decays exponentially in the commit width, so the radius is one and speculation adds no error floor. We falsify that reduction shot by shot and find the real mechanism, clearest at near-threshold noise, is a global minimum-weight re-pairing. A compiler pass derives SWIPER's restart policy from these numbers; a runtime executor confirms on the harness that the loop recovers exactly and removes the serial commit-chain stall up to a small penalty. A second decoder (union-find) settles which results are decoder-agnostic: the predict-verify-recover wrapper and the structural phenomenology, while the absolute magnitudes and the min-weight mechanism are matching-specific.
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Quantum Physics · Cross-listed from physics.chem-ph
Challenges in the simulation of enzymatic transition states with emerging multireference character
Valentin Kasper, Sanjoy Ray and Matthias Kaiser
Highly successful drugs, such as transition-state inhibitors, were designed by mimicking the precise geometry of enzymatic transition states, a strategy that requires
quantum chemistry accurate enough to specify molecular structure at sub-Å\ resolution. A central challenge during such a
quantum chemistry simulation is that classical single-reference method can deviate substantially from the exact energy at strongly correlated transition states. We study the breakdown due to multireference character by studying a model system with a multireference transition state. In this work we present a proprietary PexMachina solver which reproduces the exact ground-state energy throughout the transition state scan, while single-reference methods struggle for certain geometries to achieve chemical accuracy.
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Quantum Physics
Explaining the magnitude of Chirality-Induced Spin Selectivity via electron-electron exchange
Bence Csakany and Alex J. W. Thom
Chiral molecular structure can couple to electron
spin, leading to unexpected
spin polarization effects. This Chirality-Induced
Spin Selectivity (CISS) was first reported for DNA molecules adsorbed on gold but its microscopic origin remains unclear. We demonstrated though simulation that the exchange arising from electron-electron Coulomb interactions within the self-consistent mean field (Hartree–Fock) approximation can yield significant ($\sim 2\%$)
spin polarisation for $3$-methylcyclohexanone adsorbed on Cu(111) amplifying a much smaller ($\sim 0.0014\%$) initial bias, consistent with experiment.
Symmetry considerations ensure the result is physically meaningful, while its ab-initio nature ensures all parameters are physically realistic. This amplification is connected to existing studies on
spin-
symmetry breaking in Hartree–Fock, providing a new pathway for understanding the magnitude of CISS as an emergent phenomenon of interacting electrons.
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Quantum Physics
A "squeezed polaron" variational wavefunction for the spin boson model
Diego Barberena and Nigel Cooper
The localization transition of the sub-Ohmic
spin-
boson model generates
boson bath correlations that are, at low frequencies, analytically inaccessible to standard coherent-state-polaron variational ansatzes. In this paper, we introduce a “squeezed polaron” wavefunction incorporating generic Gaussian
boson-
boson correlations induced by the
spin impurity. This gives the correct critical power-law scaling of bath observables near the localization transition together with a systematically improved ground state energy and a more accurate determination of the critical coupling. Our wavefunction captures the correct mean-field nature of the transition in the deep sub-Ohmic region. It also displays non-mean-field critical exponents in the shallow sub-Ohmic regime. Using the squeezed polaron as a starting point, we derive scattering phase shifts for
bosons, and show how they encode the emergent energy scale that vanishes at the localization transition.
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Quantum Physics
How thermal is a filtered state?
Yilun Yang, J. Ignacio Cirac and Mari Carmen Bañuls
Quantum many-body states with sufficiently low energy variance can serve as approximations to thermal states, and they may be prepared by energy filtering simple pure states. In this work, we examine how narrow the filter width must be to guarantee thermal behavior. To this end, we analyze the problem in the Floquet regime, where filtered states are found to be equivalent to time averages. This equivalence allows us to reproduce the distinct Rényi-$\alpha$
entropy scalings as reported in [Morettini et al., Physical Review Letters 133, 240401 (2024)]. Crucially, we show that under the Floquet eigenstate thermalization hypothesis, the trace distance between Floquet-filtered states and thermal states is bounded by the square root of filter width. We further demonstrate that these results extend naturally to the conventional
Hamiltonian setting by mapping
Hamiltonian-filtered states to their Floquet counterparts.
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Quantum Physics
Universal spin-squeezing dynamics in spinor condensates
Nikolaos Giovanoudis, Navid Kazemiseresht, Fabio Mezzacapo et al. (+2 more)
The production of large-scale entangled states is one of the main goals of next-generation
quantum technologies, with an immediate potential for applications in the context of
entanglement-assisted
quantum sensing. A very promising platform to achieve this goal is offered by ultracold spinor gases, made of atoms with a large internal
spin sensitive to
magnetic fields. Here we show that the native
spin-changing collisions in a spinor Bose-Einstein condensate, combined with an arbitrary quadratic Zeeman shift, can generate scalable
spin squeezing in the collective
spin of the ensemble, following the universal paradigm of the celebrated one-axis-twisting model. Squeezing dynamics is driven by the quadratic Zeeman shift when this shift is small; and by the
spin-changing collisions for large shifts, in the form of stroboscopic squeezing. Turning off the Zeeman shift freezes out the collective-
spin dynamics, so that the ensuing collective
spin dynamics can be uniquely governed by an external field to be sensed. Our theoretical results pave the way for the use of spinor Bose gases with a large
spin in fundamental studies of
entanglement, as well as in advanced metrological applications.
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All authors Nikolaos Giovanoudis, Navid Kazemiseresht, Fabio Mezzacapo, Emilia Witkowska, Tommaso Roscilde
Quantum Physics
Entanglement-assisted remote energy transfer
Bashir Mojaveri, Rasoul Jafarzadeh Bahrbeig, Mohammad Ali Fasihi et al. (+1 more)
Currently, remote energy transfer and immunity to dissipation are hot topics in
quantum batteries (QBs). In this work, we propose a protocol to realize energy transfer between two remote atoms (a
quantum charger and a
quantum battery) each coupled to a separate optical cavity with the cavities connected by a fiber. The cavities and fiber are coupled to their individual baths. After optimizing inter-system couplings to achieve an efficient transfer, we uncover the effect of suppressing dissipation by introducing parity deformation of the cavities fields. We also prove that the charger-battery
entanglement is a consumable resource for energy storage: it is initially stored until the charger and battery reach energy balance, and then subsequently consumed to maintain the increase in energy stored in the battery. The present scheme is the first execution of energy transfer to a distant battery assisted by
entanglement, which may help better understand
quantum thermodynamics and open new possibilities toward harnessing decoherence as a resource to improve the charging performance of QBs.
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All authors Bashir Mojaveri, Rasoul Jafarzadeh Bahrbeig, Mohammad Ali Fasihi, Nasrin Abdi
Quantum Physics
Secret Key Rate Analysis of Distribution Matching Algorithms for Discrete-Modulated CV-QKD
Micael Dias, Caroline Alves, Gabrielly Roman et al. (+1 more)
Continuous variable
quantum key distribution protocols (CV-QKD) with discrete modulation have been intensively investigated to bridge the gap between ideal Gaussian modulation and modern coherent optical communication systems. To mitigate the penalty of discrete modulation, probabilistic constellation shaping (PCS) is applied to the modulation format and is typically performed by distribution matching (DM)
algorithms. In this paper, we address the application of DM
algorithms to perform PCS in CV-QKD protocols. We investigate the impact of approximating optimized Maxwell-Boltzman distributions with DM
algorithms based on Huffman (HDM) and constant composition (CCDM) codes on the protocol's secret key rate (SKR) and tolerance to excess noise. Our results show that specifically symbol-by-symbol HDM degrades the SKR by at least 30%, whereas CCDM matches the optimal SKR with code length of $10^3$ or more symbols. Furthermore, we also provide a statistical analysis of symbol dependence for both approaches, showing that CCDM must operate with blocks of at least $10^5$ symbols for the correlations become negligible. Finally, we propose an
algorithm to generate independent symbols following near-optimal distributions.
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All authors Micael Dias, Caroline Alves, Gabrielly Roman, Søren Forchhammer
Quantum Physics · Cross-listed from cs.AI
QANTIS: Hardware-Calibrated Sequential POMDP Belief Updates on IBM Heron
Bayram Yuksel Eker, Suayb S. Arslan, Ozgur Nazli et al. (+2 more)
Autonomous systems under partial observability act on beliefs, not raw sensor events. QANTIS treats the
quantum processor as a calibrated belief-update service in that loop: it receives a prior and an observation model, estimates the rare-event evidence term, and returns an ordinary posterior to a classical planner. This paper asks whether that service can be reused across a sequential Tiger POMDP horizon on present IBM Heron hardware without corrupting the planner-facing posterior. We answer with a controlled hardware case study rather than an end-to-end autonomy or wall-clock speedup claim. The study compares no amplification, guarded Grover amplification, and all-step fixed-point amplification on the same trajectory, then checks whether the returned posterior would change the downstream action. All-step FPAA preserves the Tiger posterior across the reported 8-step and 12-step primary runs, and the 20-step and 32-step controls remain inside the same operating band. In every reported decision check, the hardware posterior and the exact Bayes posterior select the same immediate action. Boundary-aware BIQAE stabilizes amplitude estimation near zero and near one, while a rare-event sweep maps the logical sample-complexity envelope for one-in-a-million evidence. The result is an operating envelope for a hardware-calibrated belief-update primitive, not a standalone hardware-advantage claim.
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All authors Bayram Yuksel Eker, Suayb S. Arslan, Ozgur Nazli, Mustafa Serhat Demirgil, Furkan Deligoz
Quantum Physics
Feynman's clock and hierarchy-informed sampling for quantum error mitigation
Theo Saporiti
Near-term physical implementations of
quantum algorithms require efficient
quantum error mitigation schemes to reduce
quantum noise. In this letter we propose a new mitigation technique, by extending the applicability of our BBGKY-ISM scheme from
quantum simulations of
spin chains to arbitrary
quantum circuits. We map executions of
quantum circuits using Feynman's clock
Hamiltonian to the
Hamiltonian dynamics of a corresponding
quantum system, whose time
evolution obeys a BBGKY-like hierarchy of equations informing the BBGKY-ISM mitigation. We show that the method's classical and
quantum overheads are
polynomial in the
circuit size and in the number of
qubits. We apply our method to numerical simulations of tunable Bell state preparation
circuits under state-of-the-art
quantum noise, and numerically demonstrate its systematic and controllable
quantum error reduction capability.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
Majorana physics in a Luttinger liquid with attractive interactions
Francesco Debortoli, Nitya Cuzzuol, Luca Barbiero et al. (+1 more)
Majorana zero modes are the hallmark of topological superconductivity. In one-dimensional systems, these zero modes are usually introduced in the context of gapped, mean-field models that do not conserve particle number, such as the Kitaev chain. By non-locally encoding a conventional
fermion across spatially separated Majorana zero modes, these systems become inherently immune to local decoherence. In this work, we show that signatures of Majorana edge physics persist in a number-conserving, gapless Luttinger
liquid of spinless
fermions with short-range attractive interactions. We identify the two-point correlator as a sharp diagnostic, revealing an edge-to-edge revival whose sign depends on the
fermion-number parity. This revival is robust in the thermodynamic limit, and persists in the excited states of the system and at different fillings. A simple particle-hole ansatz for the ground state of the system with an odd number of
fermions captures the physics of the system for a wide range of interaction strengths, interpolating between the free-
fermion limit and the strongly interacting Majorana regime. Finally, we propose a concrete protocol to realize this model with ultracold dipolar molecules or atoms in an optical
lattice, and to detect the revival via beam-splitter interferometry, opening an experimental route to Majorana physics beyond the conventional gapped-
superconductor paradigm.
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All authors Francesco Debortoli, Nitya Cuzzuol, Luca Barbiero, Fabian Grusdt
Quantum Physics
Quantum error correction of a grid-state qubit with state preparation and measurement errors below $10^{-3}$
Sara Turcotte, Lucas St-Jean, Amélie L. Pessonneaux et al. (+10 more)
Grid state
qubits offer a hardware-efficient approach to large-scale fault-tolerant
quantum computing. They access the information redundancy required for
quantum error correction by exploiting the large
Hilbert space naturally available in harmonic oscillators. Superconducting architectures are particularly suitable to implement grid state
qubits due to their fast and high-fidelity operations. Grid states in superconducting
circuits enable
quantum error correction (QEC) with performance beyond break-even. However, the state preparation and measurements (SPAM) errors of grid states has been a significant limitation to computational performances. In this work, we leverage high-performance QEC to enable repeat-until-success state preparation of both cardinal and magic states of the single-mode grid-state
qubit. We combine this with an improved measurement protocol that corrects for both finite-energy envelope and auxiliary
qubit readout errors, and increases robustness to
photon loss. Our experiments, using both techniques, achieve a combined state-preparation and measurement error below $10^{-3}$. This represents two orders-of-magnitude improvement over the state of the art, bringing this platform on par with standard SPAM error levels measured in transmon
qubits.
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All authors Sara Turcotte, Lucas St-Jean, Amélie L. Pessonneaux, Ross Shillito, Bohdan Kulchytskyy, Eliott Ouellet, Jean Olivier Simoneau, Florian Hopfmueller, Matthew Hamer, Pascal Lemieux, Dany Lachance-Quirion, Baptiste Royer, Nicholas E. Frattini
Quantum Physics · Cross-listed from cond-mat.mes-hall
Mesoscopic routers and single-pole double-throw switches for electronic heat
José Balduque and Rafael Sánchez
The unavoidable dissipation of heat in electronic nanostructures is a crucial problem, specially when their operation requires low temperatures. It demands finding devices able to control and redirect the excess heat, ideally without perturbing the electrostatic environment. We propose three-terminal junctions working either as thermal routers or as thermal single-pole double-throw switches controlled by a single external knob. Two models are discussed based on resonant tunneling energy filters and different couplings to the heat source: (i) Phase-coherent contact via a scanning tip modulates the relative amount of the two output currents via position-dependent
quantum interference; (ii) Coupling via a gate voltage tunable filter selectively switches one of the currents in the presence of dephasing. In the later case, we find that the heat flow using ideal filtering is bounded by fourth the open conductor current.
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Quantum Physics · Cross-listed from cond-mat.stat-mech
Local Markov Order and Global Inference in Many-Body Dynamics
Thomas Iadecola
We consider how the presence of conserved charges affects
memory in a classical
stochastic process, the symmetric exclusion process, with an observer constantly measuring a single site. We find that the observer's measurement record becomes Markovian (i.e., loses
memory) on a timescale that depends on their knowledge of the global charge, namely the total particle number. In particular, when the global charge is unknown a priori, the observer's time series Markovianizes on a timescale constrained by their ability to learn it from their measurement record. Augmenting the observer's record with bulk measurements drives a charge-learnability transition between charge-fuzzy and -sharp phases. We show that the
memory timescale tracks the learnability timescale, diverging in the fuzzy phase and remaining finite in the sharp phase.
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Quantum Physics
Universal purification dynamics of monitored Clifford circuits
Beatrice Magni, Federico Gerbino, Xhek Turkeshi et al. (+1 more)
Quantum circuits under sufficiently weak monitoring purify on a timescale $T_P$ exponentially long in the system size. This slowness underlies a universal purification dynamics, whose quantitative description has so far required the replica trick, with a delicate analytic continuation. We show that monitored Clifford
circuits on $L$ qudits of
prime dimension $q$ bypass this construction entirely: in the scaling limit at fixed $x = t/T_P(L)$, purification reduces to the Markovian decay of the density-
matrix rank, an exactly solvable death process descending from infinity. We compute the full scaling functions in compact form: all Rényi
entropies collapse onto a universal curve $\langle S(x) \rangle$. Exact stabilizer simulations at $q=2,3,5$ confirm the predictions, with no fitting parameter for the global model and $T_P$ as the only fitted scale for local brick-wall
circuits. Also, the replica problem amounts to a tilted version of the same Markov process, in agreement with exact computations from the Clifford commutant. Finally, the quantization of the rank leaves two hallmarks that distinguish Clifford dynamics from generic monitored
circuits: the
entropy fluctuations saturate at short scaled times $x\to0$ to an $O(1)$ variance, instead of vanishing, and observables develop a temporal modulation periodic in $\log_q x$, which cannot be captured by the replica approach.
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All authors Beatrice Magni, Federico Gerbino, Xhek Turkeshi, Andrea De Luca
Quantum Physics
Semi-Device-Independent Quantum Key Distribution from Operational Assumptions
Anubhav Chaturvedi, Giuseppe Viola, Ekta Panwar et al. (+2 more)
Semi-device-independent
quantum key distribution leaves the measurement devices uncharacterized while placing a trusted assumption on Alice's source. We formulate this source assumption operationally on Alice's four-preparation ensemble as a scalar bound on one of four physically motivated source tasks: full-label guessing, parity guessing, or their normalized composites with label exclusion. For the two-bit random-access code, we derive the exact classical frontier for each of the four source assumptions. Numerically, the BB84 strategy attains the maximal
quantum deviation from all four frontiers, while the preparation-depolarized BB84 family and the direct-sum label-leakage family trace complementary branches of the arbitrary-dimensional
quantum boundary for the two exclusion-assisted assumptions. Because all four task values are monotone under input-independent
quantum channels, the same scalar source bound constrains every Bob–Eve extension compatible with the complete observed behavior. Using a three-setting extension that separates RAC testing from key generation, we obtain two dimension-independent security certificates over this feasible set: lower bounds on the conditional min-
entropy and conditional von Neumann
entropy, obtained respectively by direct optimization of Eve's key-guessing probability and by prepare-and-measure semidefinite relaxations based on the Brown–Fawzi–Fawzi variational bound. The exclusion-assisted assumptions certify positive key rates down to nearly vanishing preparation visibility, far beyond full-label or parity guessing alone. Under direct-sum label leakage, all four independently optimized rate bounds remain positive at every sampled incomplete-leakage point and vanish only at complete label revelation. These results show that robust semi-device-independent security depends not only on what Eve can identify, but also on what she can exclude.
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All authors Anubhav Chaturvedi, Giuseppe Viola, Ekta Panwar, Tushita Prasad, Debashis Saha
Quantum Physics
Spectral Born machines: classically trainable quantum generative models for discrete data
Austin Huang, William Maxwell, Vasilis Belis et al. (+4 more)
We present spectral Born machines, a class of
quantum generative models that results from viewing and generalizing the class of IQP Born machines through the lens of group
Fourier analysis. These
quantum models exploit the
quantum Fourier transform to create an inductive bias that make them naturally suited to learning integer-structured data, while remaining classically hard to sample from in general. Similar to IQP Born machines, spectral Born machines can be trained efficiently at scale on classical hardware via a maximum mean discrepancy loss based on graph spectral analysis, which we make available in a new tcdq module of the PennyLane software platform. In numerical experiments, we show how the spectral bias of the model leads to significantly reduced parameter counts compared to unstructured approaches, and demonstrate the scalability of the software by training a 190-
qubit model with over 1 million parameters to successfully learn a distribution of 93 nucleotide-long ribosomal RNA. Our results suggest that highly over-parameterized spectral Born machines may be immune to overfitting, even in strongly data-scarce regimes.
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All authors Austin Huang, William Maxwell, Vasilis Belis, Evan Peters, Jason Pye, Soran Jahangiri, Joseph Bowles
Quantum Physics
Spin singlets are useful
Silas Hoffman, Edward H. Chen, Matthew Brooks et al. (+6 more)
We evaluate the utility of the
spin-zero
manifold of an exchange-coupled array of $N$
spins for tasks in
quantum computation and
quantum simulation. Since pairs of electrons can be readily initialized into a product state of singlets in semiconducting
quantum dot arrays, the full
spin-zero
manifold is available with exchange-only control, providing a
Hilbert space of approximate dimension $2^N/(N/2)^{3/2}$, asymptotically close to the $2^N$ dimension of the full
spin Hilbert space. Leveraging the
spin-zero
manifold enables larger computational space in a given array compared to traditional exchange-only control, in which
spin arrays are organized into modular units of $n$
spins comprising $N/n$ encoded
qubits, limiting to the exponentially smaller
Hilbert dimension $2^{N/n}$. Here we focus on benchmarking metrics for this resource utilization by generalizing cross-
entropy benchmarking, mirror benchmarking, and out-of-time-ordered correlators to this system. We show that operating in the
spin-zero
manifold can accelerate the realization of computational
quantum advantage applications in
semiconductor-based
spin qubits.
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All authors Silas Hoffman, Edward H. Chen, Matthew Brooks, Stephen Carr, Daniel Volya, Alan Tran, Tyler Keating, Thaddeus D. Ladd, Charles Tahan
Quantum Physics
Localized Thermometry via Dayem Bridges Integrated on Superconducting Qubit Chips
Ella O. Lachman, Dave P. Pappas, Jayss Marshall et al. (+1 more)
Accurate knowledge of the on-chip temperature is essential for understanding and optimizing the performance of superconducting
qubits, yet direct thermometry at millikelvin temperatures remains challenging. While
qubits themselves are sensitive to the temperature of their environment, other factors may affect the
qubits` effective temperature, and using them as thermometers with any accuracy requires specialized measurement protocols and
qubit designs, limiting their practicality for routine diagnostics and adding complex infrastructure to any hardware testing apparatus. Here we demonstrate a complementary on-chip thermometry method based on superconducting Dayem bridges that are integrated on the same chip as transmon
qubits. By extracting the critical current of the Dayem bridge from I-V measurements, we obtain a local, quantitative measure of the chip temperature without the need for microwave calibration or
qubit-specific control sequences. To demonstrate the utility of the Dayem bridges as thermometers, we fabricate them in-situ with
qubits on the same chip, calibrate the Dayem bridge critical current as a function of temperature, and characterize its resolution and stability at cryogenic temperatures. We additionally perform simultaneous measurements of the Dayem bridge thermometer and
qubit excited-state population, and show agreement over the relevant temperature range, validating the method against established
qubit thermometry. Furthermore, we correlate the independently measured chip temperature with
qubit energy relaxation and dephasing times, demonstrating the utility of this approach for diagnosing temperature-dependent decoherence mechanisms. These results establish integrated Dayem bridges as a simple, non-invasive, and scalable tool for cryogenic hardware development, and on chip thermometry in superconducting
quantum circuits.
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All authors Ella O. Lachman, Dave P. Pappas, Jayss Marshall, Josh Y. Mutus
Quantum Physics
Localized control of large ion crystals in a Penning trap using a spatial light modulator
Allison L. Carter, Jennifer F. Lilieholm, Bryce B. Bullock et al. (+3 more)
Penning ion traps as
quantum platforms have primarily utilized global control and symmetric Dicke states for
quantum simulation and sensing experiments. The introduction of local control greatly increases the power of the platform as a
quantum simulator but is technically challenging due to the rapid rotation of the ion
crystals. Here we use an ultraviolet-compatible spatial light modulator (SLM) to imprint programmable AC Stark shift patterns with different azimuthal
symmetries and gradients that co-rotate with the ion
crystals, demonstrating localized coherent control of single plane
crystals with greater than 100 ions. Comparisons of the measured ion
qubit populations with calculations from independent measurements of the applied AC Stark shift patterns show good agreement, validating the technique and providing a path, with a higher format SLM, for parallelizable, coherent individual ion addressing in Penning traps.
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All authors Allison L. Carter, Jennifer F. Lilieholm, Bryce B. Bullock, Kurt Thompson, Diep Nguyen, John J. Bollinger
Quantum Physics
Real-Time VPN Traffic over ETSI GS QKD 014 Key Delivery with a LuxQuanta NOVA QKD Platform
Felipe Paixão, Anderson Altair Tomkelski, Marcus Elias Silva Freire et al. (+5 more)
This report presents a prototype VPN that uses QKD-derived keys delivered through the ETSI GS QKD 014 API. The VPN encrypts IP traffic with AES-256-GCM, transports ETSI key identifiers in-band, and retrieves matching keys from local KMEs. After validation with a controlled KME simulator, the system was tested on two Jetson Xavier NX devices connected to a LuxQuanta NOVA QKD platform. The experiment successfully transmitted bidirectional real-time audio and
video traffic through the VPN for eight continuous hours, demonstrating the feasibility of integrating classical VPN applications with QKD infrastructure through a standardized key-delivery interface.
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All authors Felipe Paixão, Anderson Altair Tomkelski, Marcus Elias Silva Freire, Isys Nogueira de Sant'Anna, Adriano Humberto de Oliveira Maia, Reinan da Silva Salazar, Ney Ricardo Lopez Junior, João Marcelo Silva Souza
Quantum Physics
Tianhan Liu, Fedor Simkovic IV and Martin Leib
We introduce a
quantum algorithmic framework based on probabilistic mixtures of
unitary channels that, similar to the framework of
quantum singular value transformations, enables the application of arbitrary
polynomials of hermitian operators onto arbitrary initial states. We show that our framework supports a flexible tradeoff between sample- and query complexity ranging from optimal query complexity, meaning logarithmic in the error, and exponentially scaling sample complexity to sub-
polynomial query complexity in the error and
polynomial sample complexity. Combined with the considerably lower
quantum circuit complexity, compared to
quantum singular value transformations with a linear combination of
unitaries block encoding, we argue that our framework can be seamlessly scaled from NISQ to fault-tolerant
quantum computing.
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Quantum Physics
Continuous Narrow-Linewidth Superradiance in Waveguide QED
Anna Bychek, Martin Fasser, Ivan Vybornyi et al. (+4 more)
Superradiant
lasers promise continuous, narrow-linewidth coherent emission at the bare atomic transition frequency, enabling frequency references of exceptional precision. Recent experiments have advanced the field, but achieving truly continuous operation remains technically challenging. Here we propose an alternative route to an active optical frequency reference with fewer emitters using all-to-all dipole-dipole interactions mediated by a nanophotonic waveguide. We show that selectively pumping only a sub-ensemble of emitters, rather than the full ensemble, substantially improves emission characteristics. The collective interactions with unpumped emitters provide narrowband frequency selection and establish an effective feedback mechanism analogous to the role of a macroscopic cavity. We find directional superradiant emission with strongly phase-synchronized emitter correlations and a narrow output spectrum close to the bare emitter resonance. Our results demonstrate a strong metrological gain from selective partial pumping of
quantum emitters with the second-order intensity correlation $g^{(2)}(0)\simeq 1$, indicating reduced equal-time intensity fluctuations, and open a route to waveguide-based optical frequency references using small clock-atom ensembles for chip-scale precision metrology.
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All authors Anna Bychek, Martin Fasser, Ivan Vybornyi, Klemens Hammerer, Susanne F. Yelin, Helmut Ritsch, Raphael Holzinger
Quantum Physics
Quantum state localization in dipole-dipole interacting disordered networks
Pritam Chattopadhyay, Saikat Sur, Avijit Misra et al. (+3 more)
We study the localization of excitations in positionally disordered
spin or atom networks coupled via the realistic resonant dipole-dipole interaction (RDDI), which does not conform to a simple power law, as the spatial dependence and dissipative character distinguish it from conventional short or long-range models. Despite its partially long-ranged and radiative nature, positional disorder in the RDDI coupling leads to strong spatial localization of excitations. The interplay between coherent and dissipative couplings gives rise to nontrivial interference effects that stabilize localized modes even in open geometries. Our results uncover a
photon wavelength-induced transition from extended to localized excitation dynamics, establishing RDDI networks as a unique setting to explore the emergence of localization in realistic
quantum optical systems. Our analysis of the localized modes induced by RDDI has potential applications in coherent photovoltaics, excitonic
circuits,
quantum memory, and
quantum sensors.
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All authors Pritam Chattopadhyay, Saikat Sur, Avijit Misra, David Petrosyan, Arti Garg, Gershon Kurizki
Quantum Physics
Differentially private quantum sensor networks
Daniel J. Spencer, Kaiyan Shi, Emil T. Khabiboulline et al. (+2 more)
Quantum sensing is a promising technology capable of demonstrating clear advantage over comparable classical techniques for precise measurement. One application of
quantum sensing is in function estimation, which can be done using a network of entangled
quantum sensors, allowing for measurements with greater optimal sensitivity than unentangled sensing protocols. In cases where
quantum sensor networks will be used to measure data that should remain private (e.g., biomedical data), it is imperative that these protocols include a
privacy mechanism to hide sensitive information. In this work, we show that entangled sensor networks are vulnerable to certain
privacy-violating attacks. To mitigate these attacks, we introduce secure sensing protocols endowed with differential
privacy. We reconcile differential
privacy with retaining Heisenberg-limited scaling, and introduce several protocols achieving varying balances between the two. We show that our main protocol, an $n$-node network sensing protocol that injects noise directly into the sensing
Hamiltonian, exhibits a tradeoff between the desirable $O(1/n^2)$ Heisenberg scaling of the mean-squared error of the function estimate and the level of
privacy attainable. Under assumptions on the network (a common source of randomness and a constant fraction of honest parties), we show that this protocol is locally implementable and achieves $(O(1), \delta)$-differential
privacy for arbitrarily small $\delta$ while retaining Heisenberg scaling of the mean-squared error. We prove that our protocols are resilient to attacks by broad classes of classical and
quantum adversaries, and find advantages in the
privacy-utility tradeoff when using
quantum techniques.
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All authors Daniel J. Spencer, Kaiyan Shi, Emil T. Khabiboulline, Gorjan Alagic, Alexey V. Gorshkov
Quantum Physics
Leveraging Metrologically Useful States in Quantum Reservoir Networks
Erik L. Connerty, Margarite LaBorde and Ethan N. Evans
Interest in using
quantum computers for the purpose of predicting chaotic partial differential equations (PDEs) has been growing with the advent of newer low-error
quantum computers and robust simulation tools. In this paper, we present a method that utilizes a
quantum reservoir network (QRN) to predict latent space representations of the high-dimensional chaotic 1-D Kuramoto-Sivashinksy (KS) system. This hybrid approach takes advantage of advancements in classical machine learning (ML) through the use of a classical autoencoder as well as techniques from
quantum metrology through the use of a
unitary that creates metrologically-useful states. Through rigorous simulation and analysis, we show that the proposed method outperforms alternative QRN implementations without this metrologically-useful state preparation, and also show better performance than classical echo-state networks when weight regularization is not used. Finally, we bring to light potential issues that can arise when using autoencoders within QRC pipelines.
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