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At least 505 records · Page 28

Thermalization from quantum entanglement: Jet simulations in the massive Schwinger model

We investigate the emergence of thermalization in a quantum-field-theoretic model mimicking the production of jets in QCD: the massive lattice Schwinger model coupled to external sources. Specifically, we compute the expectation values of local operators as functions of time and compare them to their thermal counterparts, quantify the overlap between the evolving density matrix and the thermal one, and compare the dynamics of the energy-momentum tensor to predictions from relativistic hydrodynamics. Through these studies, we find that the system approaches thermalization at late times and elucidate the mechanisms by which quantum entanglement drives thermalization in closed field-theoretic systems. Our results show how thermodynamic behavior emerges in real time from unitary quantum dynamics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

QuYBE - An Algebraic Compiler for Quantum Circuit Compression

QuYBE is an open-source algebraic compiler for the compression of quantum circuits. It has been applied for the efficient simulation of the Heisenberg Hamiltonian on quantum computers. Currently, it can simulate the time dynamics of one-dimensional chains. It includes modules to generate the quantum circuits for the above as well as produce the compressed circuits, which are independent of the time step. It utilizes the Yang-Baxter equation (YBE) to perform the compression. QuYBE enables users to seamlessly design, execute, and analyze the time dynamics of the Heisenberg Hamiltonian on quantum computers. QuYBE is the first step toward making the YBE technique available to a broader community of scientists from multiple domains. The QuYBE compiler is available at https://github.com/ZichangHe/QuYBE.

Gulania, Sahil↗

Classical discrete time crystals

The spontaneous breaking of time-translation symmetry in periodically driven quantum systems leads to a new phase of matter: the discrete time crystal (DTC). This phase exhibits collective subharmonic oscillations that depend upon an interplay of non-equilibrium driving, many-body interactions and the breakdown of ergodicity. However, subharmonic responses are also a well-known feature of classical dynamical systems ranging from predator–prey models to Faraday waves and a.c.-driven charge density waves. This raises the question of whether these classical phenomena display the same rigidity characteristic of a quantum DTC. In this work, we explore this question in the context of periodically driven Hamiltonian dynamics coupled to a finite-temperature bath, which provides both friction and, crucially, noise. Focusing on one-dimensional chains, where in equilibrium any transition would be forbidden at finite temperature, we provide evidence that the combination of noise and interactions drives a sharp, first-order dynamical phase transition between a discrete time-translation invariant phase and an activated classical discrete time crystal (CDTC) in which time-translation symmetry is broken out to exponentially long timescales. Power-law correlations are present along a first-order line, which terminates at a critical point. We analyse the transition by mapping it to the locked-to-sliding transition of a d.c.-driven charge density wave. To conclude, building upon results from the field of probabilistic cellular automata, we conjecture the existence of classical time crystals with true long-range order, where time-translation symmetry is broken out to infinite times.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Intersubband Auger recombination and population inversion in quantum-well subbands

The intersubband-Auger-recombination time of electrons under population-inversion conditions in a single quantum well is calculated by taking into account momentum- and energy-conservation rules, and by employing Fermi-Dirac statistics. The screened matrix element of the electron-electron interaction and the overlap integral are calculated for an infinitely deep quantum well. The results are in a good agreement with published experimental data. As a major nonradiative process, the Auger recombination is related to threshold current of infrared lasers based on intersubband transitions in quantum-well structures. The realization of these devices and other limitations to achieving population inversion are discussed. In view of the results, development of these lasers for emission wavelengths corresponding to energies below the LO-phonon energy seems feasible.

Borenstain, S.↗

New perspectives on QFT and gravity from quantum entanglement

The work accomplished by the PI as part of this award included studying the fundamental as- pects of quantum field theory (QFT) and the nature of space-time and gravity via the patterns of quantum entanglement present in these theories. By following these patterns the PI attacked basic questions on the nature of quantum gravity and found new constraints on the dynamical content of QFT. These topics find a natural home within the holographic dualiy, a deep mathemat- ical correspondence discovered in string theory where a gravitational system can be described by a quantum system without gravity. By studying the spatial distribution of quantum correlation, or entanglement, in various quantum systems the PI managed to directly observe the holographic emergence of quantum gravity within this mathematical framework. The PI also characterized the space-time structure that emerges via the duality. In achieving these aims the project shed light on the thermodynamic nature of gravity and had considerable impact on understanding of the uni- fication of gravity with quantum mechanics. Additionally, this work shed light on the structure of quantum entanglement in QFT and in so doing used powerful constraints satisfied by entanglement and it’s generalizations to place bounds on the basic data of the QFT. The project also related these bounds to causality constraints and quantum energy conditions in field theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Quantum Algorithm for Linear Non-unitary Dynamics with Near-Optimal Dependence on All Parameters

We introduce a family of identities that express general linear non-unitary evolution operators as a linear combination of unitary evolution operators, each solving a Hamiltonian simulation problem. This formulation can exponentially enhance the accuracy of the recently introduced linear combination of Hamiltonian simulation (LCHS) method [An, Liu, and Lin, Physical Review Letters, 2023]. For the first time, this approach enables quantum algorithms to solve linear differential equations with both optimal state preparation cost and near-optimal scaling in matrix queries on all parameters.

Applied Dynamical Systems↗

Comments on the Transplanckian Censorship Conjecture

We consider some aspects of the Transplanckian Censorship Conjecture (TCC), which states that for theories of quantum gravity there is a limit on the lifetime of dS or quintessence states not too different than the current Hubble horizon. If one accepts the de Sitter Swampland conjecture, then the former are ruled out. We consider some aspects of tunneling to an isolated ground state in the presence of time-varying fields, in quantum mechanics and quantum field theory in the absence of gravitation, and note that lifetimes are typically enormous; in fact, there is often a finite probability for the system to remain eternally in its original state. With gravity in a universe with superluminal expansion, while the field evolution may be slowed, Planck scale fluctuations would seem likely to grow to superhorizon size long before the universe decays. We argue that the TCC, if it is correct, requires that superluminal expansion occur only for a brief period in the history of the universe, and will be followed by a p = ρ phase.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

A Cryogenic Muon Tagging System Integrated with a Superconducting Qubit Device for Radiation-Induced Error Mitigation

Superconducting qubits are highly sensitive to ionizing radiation, which can induce correlated errors and limit scalable fault-tolerant quantum computing. In particular, cosmic-ray muons can deposit energy in the substrate, generating phonon bursts that break Cooper pairs and produce quasiparticles, leading to correlated decoherence events across multiple qubits. We present the development of a cryogenic muon tagging system based on Kinetic Inductance Detectors (KIDs) and its integration with superconducting quantum hardware. Originally developed within the ACE-SuperQ project and validated as a standalone detector, the system demonstrated a muon tagging efficiency of approximately 90% and excellent agreement with Monte Carlo simulations. Building on this validation, the tagging system has been integrated with a multi-qubit superconducting chip operated in a dilution refrigerator. The detector configuration consists of a multi-layer KID stack arranged above and below the quantum device, enabling time-coincident identification of muon-induced events within the same cryogenic environment. The integrated setup has been successfully commissioned, enabling simultaneous operation of the qubit chip and the muon tagging system. A first measurement campaign has been carried out, and preliminary data show time-correlated events between the muon tagging detectors and the qubit readout. A quantitative analysis of radiation-induced effects on qubit performance is currently ongoing. This work represents a step toward the implementation of event-level radiation tagging as a tool for characterizing and potentially mitigating correlated errors in superconducting quantum processors, while establishing a modular platform for future studies at the interface between particle physics and quantum information science.

Roy, Tanay [Fermilab] (ORCID:000000019442862X)↗

Optimal Control of Families of Quantum Gates

Quantum optimal control (QOC) enables the realization of accurate operations, such as quantum gates, and supports the development of quantum technologies. To date, many QOC frameworks have been developed, but those remain only naturally suited to optimize a single targeted operation at a time. Here, we extend this concept to optimal control with a continuous family of targets, and demonstrate that an optimization based on neural networks can find families of time-dependent Hamiltonians realizing desired classes of quantum gates in minimal time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Ion trap long-range XY model for quantum state transfer and optimal spatial search

Abstract Linear ion trap chains are a promising platform for quantum computation and simulation. The XY model with long-range interactions can be implemented with a single side-band Mølmer–Sørensen scheme, giving interactions that decay as 1 / r α , where α parameterises the interaction range. Lower α leads to longer range interactions, allowing faster long-range gate operations for quantum computing. However, decreasing α causes an increased generation of coherent phonons and appears to dephase the effective XY interaction model. We characterise and show how to correct for this effect completely, allowing lower α interactions to be coherently implemented. Ion trap chains are thus shown to be a viable platform for spatial quantum search in optimal O ( N ) time, for N ions. Finally, we introduce a O ( N ) quantum state transfer protocol, with a qubit encoding that maintains a high fidelity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Computational Performance Bounds Prediction in Quantum Computing With Unstable Noise

Quantum computing has significantly advanced in recent years, boasting devices with hundreds of quantum bits (qubits), hinting at its potential quantum advantage over classical computing. Yet, noise in quantum devices poses significant barriers to realizing this supremacy. Understanding noise’s impact is crucial for reproducibility and application reuse; moreover, the next-generation quantum-centric supercomputing essentially requires efficient and accurate noise characterization to support system management (e.g., job scheduling), where ensuring correct functional performance (i.e., fidelity) of jobs on available quantum devices can even be higher-priority than traditional objectives. However, noise fluctuates over time, even on the same quantum device, which makes predicting the computational bounds for on-the-fly noise is vital. Noisy quantum simulation can offer insights but faces efficiency and scalability issues. Here, in this work, we propose a data-driven workflow, namely QuBound, to predict computational performance bounds. It decomposes historical performance traces to isolate noise sources and devises a novel encoder to embed circuit and noise information processed by a Long Short-Term Memory (LSTM) network. For evaluation, we compare QuBound with a state-of-the-art learning-based predictor, which only generates a single performance value instead of a bound. Experimental results show that the result of the existing approach falls outside of performance bounds, while all predictions from our QuBound with the assistance of performance decomposition better fit the bounds. Moreover, QuBound can efficiently produce practical bounds for various circuits with over 106 speedup over simulation; in addition, the range from QuBound is over 10× narrower than the state-of-the-art analytical approach.

Li, Jinyang [George Mason Univ., Fairfax, VA (Unit↗

Point defects in semiconductors: Friends and foes for quantum technologies

Point defects in semiconductors are both a curse and a blessing in microelectronics: they enable the control of electrical conductivity through doping, yet can also act as trapping and recombination centers that degrade device performance. In quantum information science, defects play a similarly dual role. They can be harnessed as spin–photon interfaces enabling the coupling of electronic and nuclear spins to light and the creation of distributed entanglement for quantum networks or used as atomistic scale sensors for quantum sensing. At the same time, defects are a major source of decoherence for superconducting qubits, one of the leading quantum computing platforms. This article discusses how a deeper materials-level understanding of defects can guide the design of improved quantum devices for communication, sensing, and computation.

Zhu, Yizhi [Rice University, Houston, TX (United S↗

Space QUEST Mission Proposal: Experimentally Testing Decoherence Due to Gravity

Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum properties, such as entanglement, may exhibit entirely different behavior to purely classical systems. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph and coworkers [T C Ralph, G J Milburn, and T Downes, Phys. Rev. A, 79(2):22121, 2009; T C Ralph and J Pienaar, New Journal of Physics, 16(8):85008, 2014], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's (ESA) Space QUEST (Space - Quantum Entanglement Space Test) mission, and study the feasibility of the mission schema.

Entanglement↗

Slow spin relaxation in single endohedral fullerene molecules

Well-protected magnetization, tunable quantum states, and long spin-relaxation time are desired for the use of magnetic molecules in spintronics and quantum information technologies. In this work, endohedral fullerene molecules M@C 28 with different transition-metal cores were explored through systematic first-principles calculations and spin dynamics analyses. Many of them have bias-tunable structure, stable magnetization, and sizable magnetic anisotropy energy. Furthermore, some of them may have spin-relaxation time up to several milliseconds for their quantum spin states at high temperature (~10 K) after full consideration of spin-vibration couplings. In conclusion, our results suggest that these M@C 28 provide a rich pool of single-molecule magnets for diverse applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Biexciton and trion dynamics in InP/ZnSe/ZnS quantum dots

Transient absorption (TA) and time-resolved photoluminescence (PL) spectroscopies have been used to elucidate the hole tunneling and Auger dynamics in biexcitons and negative trions in high-quality InP/ZnSe/ZnS quantum dots (QDs). In a previous paper [Nguyen et al., J. Phys. Chem. C 125, 15405–15414 (2021)], we showed that under high-intensity photoexcitation, two types of biexcitons are formed: those having two conduction band electrons and two valence band holes (designated as an XX state) and those having two conduction band electrons, one valence band hole, and an additional trapped hole (designated as an XT state). In the present paper, we show that both types of biexcitons can undergo Auger processes, with those of the XT state being a factor of four to five slower than those of the XX state. In addition, the trapped holes can undergo tunneling into the valence band, converting an XT state to an XX state. The relative amplitudes of the fast (XX) and slow (XT) components are different in the TA and PL kinetics, and these differences can be quantitatively understood in terms of oscillator strengths and electron–hole overlap integrals of each state. XT to XX hole tunneling rates are obtained from the comparison of the XT state lifetimes with those of the negative trions. This comparison shows that the tunneling times decrease with decreasing core size and shell thickness. Furthermore, these times are about 2 ns for the thinnest shell red-emitting QDs and decrease to 330 ps for QDs that luminesce in the yellow.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Algebraic compression of quantum circuits for Hamiltonian evolution

Here unitary evolution under a time-dependent Hamiltonian is a key component of simulation on quantum hardware. Synthesizing the corresponding quantum circuit is typically done by breaking the evolution into small time steps, also known as Trotterization, which leads to circuits the depth of which scales with the number of steps. When the circuit elements are limited to a subset of SU(4) - or equivalently, when the Hamiltonian may be mapped onto free fermionic models - several identities exist that combine and simplify the circuit. Based on this, we present an algorithm that compresses the Trotter steps into a single block of quantum gates using algebraic relations between adjacent circuit elements. This results in a fixed depth time evolution for certain classes of Hamiltonians. We explicitly show how this algorithm works for several spin models, and demonstrate its use for adiabatic state preparation of the transverse field Ising model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

High-fidelity remote entanglement of trapped atoms mediated by time-bin photons

Abstract Photonic interconnects between quantum processing nodes are likely the only way to achieve large-scale quantum computers and networks. The bottleneck in such an architecture is the interface between well-isolated quantum memories and flying photons. We establish high-fidelity entanglement between remotely separated trapped atomic qubit memories, mediated by photonic qubits stored in the timing of their pulses. Such time-bin encoding removes sensitivity to polarization errors, enables long-distance quantum communication, and is extensible to quantum memories with more than two states. Using a measurement-based error detection process and suppressing a fundamental source of error due to atomic recoil, we achieve an entanglement fidelity of 97% and show that fundamental limits due to atomic recoil still allow fidelities in excess of 99.9%.

Science & Technology - Other Topics↗

Search for quantum black hole production in lepton + jet final states using proton-proton collisions at s = 13 TeV with the ATLAS detector

A search for quantum black holes in electron + jet and muon + jet invariant mass spectra is performed with 140 fb -1 of data collected by the ATLAS detector in proton-proton collisions at $\sqrt{s}$ =13 TeV at the Large Hadron Collider. The observed invariant mass spectrum of lepton + jet pairs is consistent with Standard Model expectations. Upper limits are set at 95% confidence level on the production cross section times branching fractions for quantum black holes decaying into a lepton and a quark in a search region with invariant mass above 2.0 TeV. The resulting quantum black hole lower mass threshold limit is 9.2 TeV in the Arkani-Hamed-Dimopoulos-Dvali model, and 6.8 TeV in the Randall-Sundrum model.

79 ASTRONOMY AND ASTROPHYSICS↗