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Results for “quantum quench”

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Quenched lattice fluctuations in optically driven SrTiO3

Abstract Crystal lattice fluctuations, which are known to influence phase transitions of quantum materials in equilibrium, are also expected to determine the dynamics of light-induced phase changes. However, they have only rarely been explored in these dynamical settings. Here we study the time evolution of lattice fluctuations in the quantum paraelectric SrTiO 3 , in which mid-infrared drives have been shown to induce a metastable ferroelectric state. Crucial in these physics is the competition between polar instabilities and antiferrodistortive rotations, which in equilibrium frustrate the formation of long-range ferroelectricity. We make use of high-intensity mid-infrared optical pulses to resonantly drive the Ti–O-stretching mode at 17 THz, and we measure the resulting change in lattice fluctuations using time-resolved X-ray diffuse scattering at a free-electron laser. After a prompt increase, we observe a long-lived quench in R-point antiferrodistortive lattice fluctuations. Their enhancement and reduction are theoretically explained by considering the fourth-order nonlinear phononic interactions to the driven optical phonon and third-order coupling to lattice strain, respectively. These observations provide a number of testable hypotheses for the physics of light-induced ferroelectricity.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Optical Properties of Tm(3+) Ions in Alkali Germanate Glass

Tm-doped alkali germanate glass is investigated for use as a laser material. Spectroscopic investigations of bulk Tm-doped germanate glass are reported for the absorption, emission and luminescence decay. Tm:germanate shows promise as a fiber laser when pumped with 0.792 m diodes because of low phonon energies. Spectroscopic analysis indicates low nonradiative quenching and pulsed laser performance studies confirm this prediction by showing a quantum efficiency of 1.69.

Walsh, Brian M.↗
DOE OSTI2022

Semiclassical Trajectory Studies of Reactive and Nonreactive Scattering of OH( 2 Σ + ) by H 2 Based on an Improved Full-Dimensional Ab Initio Diabatic Potential Energy Matrix

Here we present a new full-dimensional diabatic potential energy matrix (DPEM) for electronically nonadiabatic collisions of OH(A 2 Σ + ) with H 2 , and we calculate the probabilities of electronically adiabatic inelastic collisions, nonreactive quenching, and reactive quenching to form H 2 O+H. The DPEM was fitted using a many-body expansion with permutationally invariant polynomials in bond-order functions to represent the many-body part. The dynamics calculations were carried out with the fewest-switches with time uncertainty and stochastic decoherence (FSTU/SD) semiclassical trajectory method. We present results both for head-on collisions (impact parameter b equal to zero) and for a full range of impact parameters. The results are compared to experiment and to earlier FSTU/SD and quantum dynamics calculations with a previously published DPEM. The various theoretical results all agree that nonreactive quenching dominates reactive quenching, but there are quantitative differences between the two DPEMs and between the b=0 results and the all-b results, especially for the probability of reactive quenching.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Adaptive variational quantum dynamics simulations with compressed circuits and fewer measurements

The adaptive variational quantum dynamics simulation (AVQDS) method performs real-time evolution of quantum states using automatically generated parametrized quantum circuits that often contain substantially fewer gates than Trotter circuits. Here we report an improved version of the method, which we call AVQDS(T), by porting the tiling efficient trial circuits with rotations implemented simultaneously technique. The algorithm adaptively adds layers of disjoint unitary gates to the ansatz circuit so as to keep the McLachlan distance, a measure of the accuracy of the variational dynamics, below a fixed threshold. Here we perform benchmark noiseless AVQDS(T) simulations of quench dynamics in local spin models and compare with an alternative adaptive variational approach on quantum resource requirement. Quantum dynamical simulations implementing realistic noise channels are also reported. Finally, we propose a way to substantially alleviate the measurement overhead of AVQDS(T) while maintaining high accuracy by synergistically integrating quantum circuit calculations on quantum processing units with classical calculations using, e.g., tensor networks to evaluate the quantum geometric tensor. We showcase that this approach enables AVQDS(T) to deliver more accurate results than simulations using a fixed ansatz of comparable final depth for a significant time duration with fewer quantum resources.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Controlling quantum many-body dynamics in driven Rydberg atom arrays

Dynamic stabilization of an array Large-scale systems comprising one-dimensional chains and two-dimensional arrays of excited atoms held in a programmable optical lattice are a powerful platform with which to simulate emergent phenomena. Bluvstein et al. built an array of up to 200 Rydberg atoms and subjected the system to periodic excitation. Under such driven excitation, they found that the array of atoms stabilized, freezing periodically into what looked like time crystals. Understanding and controlling the dynamic interactions in quantum many-body systems lies at the heart of contemporary condensed matter physics and the exotic phenomena that can occur. Science , this issue p. 1355

Science & Technology - Other Topics↗
NASA NTRS1978

Photodissociation of CO2 and quenching of metastables

Investigations in four different areas were carried out to further our understanding of the chemistry of the atmospheres of Mars and Venus. CO2 photodissociation quantum yields were determined in the 1300-1500 A spectral region by measuring both CO and oxygen atoms. The O(1S) quantum yield was determined for CO2 photodissociation in the 1060-1175 A spectral region. The measurement resolves the differences between two earlier experiments, and demonstrates that the O(1S) yield is unity throughout most of the measured region. The pathways for the quenching of O(1S) by N2O, CO2, H2O and NO were investigated and the source of the Venus nightglow, detected by Venera 9 and 10, was investigated. What appears to be a new O2 band system, was detected although the identity of the transition is not yet evident.

Slanger, T. G.↗
DOE OSTI2025

Classical signatures of quenched and thermal disorder in the dynamics of correlated spin systems

Neutron scattering is frequently used to look for evidence of features indicative of quantum-entangled phases of matter such as continua from fractionalisation or quantised excitations. However, the non-specificity of these features and difficulty of both fully quantum treatments and semiclassical models of disorder, make the diagnosis of such states problematic. Here, we demonstrate the feasibility of semiclassical treatments of disordered systems for supercells of ~10 000 spins. By examining a number of classically disordered models we show the presence of quantised excitations, broad continua and anomalous damping originating from quenched disorder or large classical degeneracies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Spin Sum Rule of the Nucleon in the QCD Instanton Vacuum

We briefly review some essential aspects of the QCD instanton vacuum in relation to the quantum breaking of conformal symmetry, the spontaneous breaking of chiral symmetry, and the axial U(1) anomaly. The anomaly causes the intrinsic nucleon spin to transmute to the vacuum topological charge by quantum tunneling. We use Ji′s invariant spin decomposition to discuss the spin budget of the nucleon as a quark–diquark state in the QCD instanton vacuum. A measure of the intrinsic quark spin of the nucleon is a measure of the quenched topological susceptibility of the QCD instanton vacuum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Coupled charge and energy transfer dynamics in light harvesting complexes from a hybrid hierarchical equations of motion approach

Here, we describe a method for simulating exciton dynamics in protein–pigment complexes, including effects from charge transfer as well as fluorescence. The method combines the hierarchical equations of motion, which are used to describe quantum dynamics of excitons, and the Nakajima–Zwanzig quantum master equation, which is used to describe slower charge transfer processes. We study the charge transfer quenching in light harvesting complex II, a protein postulated to control non-photochemical quenching in many plant species. Using our hybrid approach, we find good agreement between our calculation and experimental measurements of the excitation lifetime. Furthermore, our calculations reveal that the exciton energy funnel plays an important role in determining quenching efficiency, a conclusion we expect to extend to other proteins that perform protective excitation quenching. This also highlights the need for simulation methods that properly account for the interplay of exciton dynamics and charge transfer processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Inferring the Dynamics of the State Evolution During Quantum Annealing

To solve an optimization problem using a commercial quantum annealer, one has to represent the problem of interest as an Ising or a quadratic unconstrained binary optimization (QUBO) problem and submit its coefficients to the annealer, which then returns a user-specified number of low-energy solutions. It would be useful to know what happens in the quantum processor during the anneal process so that one could design better algorithms or suggest improvements to the hardware. However, existing quantum annealers are not able to directly extract such information from the processor. Hence, in this work we propose to use advanced features of D-Wave 2000Q to indirectly infer information about the dynamics of the state evolution during the anneal process. Specifically, D-Wave 2000Q allows the user to customize the anneal schedule, that is, the schedule with which the anneal fraction is changed from the start to the end of the anneal. Furthermore, using this feature, we design a set of modified anneal schedules whose outputs can be used to generate information about the states of the system at user-defined time points during a standard anneal. With this process, called "slicing", we obtain approximate distributions of lowest-energy anneal solutions as the anneal time evolves. We use our technique to obtain a variety of insights into the annealer, such as the state evolution during annealing, when individual bits in an evolving solution flip during the anneal process and when they stabilize, and we introduce a technique to estimate the freeze-out point of both the system as well as of individual qubits.

42 ENGINEERING↗
DOE OSTI2023

All-optical, Microwave-free NV-Diamond Magnetometer for High Magnetic Field Environment

Nitrogen vacancy (NV) magnetometry has commonly utilized microwave sources to manipulate the sensor's spin state. However, this technique becomes technically challenging under an environment with a Tesla-scale magnetic field or extreme conditions that prohibit the usage of microwave. By leveraging the effect that an off-axis magnetic field to the NV axis quenches its emitted photoluminescence, we present an all-optical, microwave-free broadband quantum diamond magnetometer. We demonstrate magnetic sensing over an extended bias magnetic field range — beyond the ground-state level anti-crossing (GSLAC) region — with a more integrated design.

Zheng, Xiechen↗
DOE OSTI2025

Heterovalent Substitution of K 2 SrP 2 O 7 :Cr 3+ to Achieve Anti-Thermal-Quenching Broadband Near-Infrared Luminescence

Broadband near-infrared (NIR) light sources based on phosphor-converted light-emitting diodes are highly desirable for biochemical analysis and medical diagnosis applications. However, thermal quenching remains a demanding challenge for developing efficient NIR phosphors. Herein, we report the enhancement of both quantum efficiency and thermal stability in Cr 3+ -activated K 2 SrP 2 O 7 phosphors through a heterovalent substitution strategy by replacing Sr 2+ with Al 3+ in K 2 Sr 1–x Al x P 2 O 7 (0.05 ≤ x ≤ 0.2) to obtain optimized broadband NIR emission. Structural modulation via Al 3+ substitution leads to the optimized composition, K 2 Sr 0.88 Al 0.1 P 2 O 7 :0.02Cr 3+ , which emits across a broad NIR range of 650–1100 nm peaking at 807 nm with a full width at half-maximum of ∼130 nm under 448 nm excitation. Remarkably, its emission intensity at 150 °C remains 120% of the initial value at room temperature, demonstrating a rare antithermal-quenching behavior. Temperature-dependent XRD studies further reveal that Al 3+ substitution effectively suppresses lattice expansion at elevated temperatures, indicating enhanced lattice stability under thermal excitation. Detailed structural and spectral analyses show that the substitution enhances local site symmetry, reduces electron–phonon coupling, increases thermally induced absorption probability, and fortifies energetic barriers against nonradiative transitions. These synergistic effects collectively endow this NIR phosphor with a superior thermal stability. Furthermore, NIR light-emitting diodes fabricated with this phosphor exhibit strong potential for applications in information identification, nondestructive detection, and night vision technologies. This study demonstrates a local structure engineering strategy for designing thermally robust Cr 3+ -activated NIR phosphors, offering valuable insights into material discovery and NIR spectroscopy device development.

Cr3+↗
DOE OSTI2020

Water-Triggered Photoinduced Electron Transfer in Acetonitrile–Water Binary Solvent. Solvent Microstructure-Tuned Reactivity of Hydrophobic Solutes

The solvent-composition dependence of quenching triplet states of benzophenone (3 BP) by anisole in acetonitrile-water (ACN-H2O) mixtures was investigated by laser flash photolysis over the water mole fraction (xw) increasing from 0 to 0.92. Single exponential decay of 3 BP was observed over the whole composition range. The quenching rate constant consistently increased with the water content but increased far more rapidly with xw > 0.7. The water-triggered electron-transfer (ET) mechanism was confirmed by a steeply growing quantum yield of the benzophenone ketyl radical anion, escaping back-ET when the partial water volume exceeded the acetonitrile one. The water-content influence on the 3 BP quenching rate was described by a kinetic model accounting for the microheterogeneous structure of the ACN-H2O mixtures and the very different solubility of the reactants in the solvent components. According to the model, the ET mechanism occurs at a rate constant of 1.46 × 109 M-1 s -1 and is presumably assisted by the ACN-H2O hydrogen-bonding interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mixed quantum/classical theory for rotational energy exchange in symmetric-top-rotor + linear-rotor collisions and a case study of the ND 3 + D 2 system

The extension of mixed quantum/classical theory (MQCT) to describe collisional energy transfer is developed for a symmetric-top-rotor + linear-rotor system and is applied to ND 3 + D 2 . State-to-state transition cross sections are computed in a broad energy range for all possible processes: when both ND 3 and D 2 molecules are excited or both are quenched, when one is excited while the other is quenched and vice versa, when the ND 3 state changes its parity while D 2 is excited or quenched, and when ND 3 is excited or quenched while D 2 remains in the same state, ground or excited. In all these processes the results of MQCT are found to approximately satisfy the principle of microscopic reversibility. For a set of sixteen state-to-state transitions available from the literature for a collision energy of 800 cm –1 the values of cross sections predicted by MQCT are within 8% of accurate full-quantum results. A useful time-dependent insight is obtained by monitoring the evolution of state populations along MQCT trajectories. It is shown that, if before the collision, D 2 is in its ground state, the excitation of ND 3 rotational states proceeds through a two-step mechanism in which the kinetic energy of molecule–molecule collision is first used to excite D 2 and only then is transferred to the excited rotational states of ND 3 . Finally, it is found that both potential coupling and Coriolis coupling play important roles in ND 3 + D 2 collisions.

inelastic cross-sections↗
DOE OSTI2024

Reductive Dynamic and Static Excited State Quenching of a Homoleptic Ruthenium Complex Bearing Aldehyde Groups

A new homoleptic Ru polypyridyl complex bearing two aldehyde groups on each bipyridine ligand, [Ru(dab) 3 ](PF 6 ) 2 , where dab is 4,4′-dicarbaldehyde-2,2′-bipyridine, was synthesized, characterized, and utilized for iodide photo-oxidation studies. In acetonitrile (CH 3 CN) solution, the complex displayed an intense metal-to-ligand charge transfer (MLCT) absorbance maximum at 475 nm (ε = 22,000 M –1 cm –1 ) and an infrared (IR) band at 1712 cm –1 assigned to the pendent aldehyde groups. Visible light excitation in air-saturated solution resulted in room temperature photoluminescence (PL) with a maximum at 675 nm, a quantum yield, ϕ PL = 0.048, and an excited state lifetime, τ ο = 440 ns, from which radiative and nonradiative relaxation rate constants were extracted, k r = 9.1 × 10 4 s –1 and knr = 1.8 × 10 6 s –1 . Pulsed visible light excitation yielded transient UV–vis and IR absorption spectra consistent with an MLCT excited state; relaxation occurred with the maintenance of two isosbestic points in the visible region, and a lifetime that agreed with that measured by time-resolved PL. Cyclic voltammetry studies in a CH 3 CN solution with 0.1 M TBAPF 6 electrolyte revealed a quasi-reversible oxidation, E°(Ru III/II ) = +1.25 V vs. Fc +/0 , and three sequential one-electron reductions at −1.10, −1.25, and −1.54 V vs. Fc +/0 . Here, an excited state reduction potential of E°(Ru *2+/+ ) = +0.89 V vs. Fc +/0 was estimated with the Rehm–Weller expression. Titration of tetrabutylammonium iodide, TBAI, into a CD 3 CN solution of [Ru(dab) 3 ](PF 6 ) 2 resulted in significant shifts in the aldehyde H atom and 3,3′-biypridyl resonances that were analyzed with a 1:1 equilibrium model, from which K eq = 460 M –1 was extracted, increasing to 5800 M –1 when the solvent was changed to acetone-d 6 . Iodide titrations resulted in a significant quenching of the [Ru(dab) 3 ] *2+ lifetime and quantum yield in both CH 3 CN and acetone solvents. In CH 3 CN, the quenching was mainly dynamic and well described by the Stern–Volmer model, from which a quenching rate constant, k q , of 4.5 × 10 10 M –1 s –1 and an equilibrium constant, K eq , of 8.3 × 10 3 M –1 were obtained. In acetone, the static quenching pathway by iodide was greatly enhanced, with a K eq of 1.2 × 10 4 M –1 and a higher k q of 9.2 × 10 10 M –1 s –1 .

Aldehydes↗
DOE OSTI2025

Perturbative Stability and Error-Correction Thresholds of Quantum Codes

Topologically ordered phases are stable to local perturbations, and topological quantum error-correcting codes enjoy thresholds to local errors. We connect the two notions of stability by constructing classical statistical mechanics models for decoding general Calderbank-Shor-Steane codes and classical linear codes. Our construction encodes correction success probabilities under uncorrelated bit-flip and phase-flip errors, and simultaneously describes a generalized ℤ 2 lattice-gauge theory with quenched disorder. We observe that the clean limit of the latter is precisely the discretized imaginary-time path integral of the corresponding quantum code Hamiltonian when the errors are turned into a perturbative 𝑋 or 𝑍 magnetic field. Motivated by error-correction considerations, we define general order parameters for all such generalized ℤ 2 lattice-gauge theories, and show that they are generally lower bounded by success probabilities of error correction. For CSS codes satisfying the low-density parity-check condition and with a sufficiently large code distance, we prove the existence of a low-temperature ordered phase of the corresponding lattice-gauge theories, particularly for those lacking Euclidean spatial locality and/or when there is a nonzero code rate. We further argue that these results provide evidence for stable phases in the corresponding perturbed quantum Hamiltonians, obtained in the limit of continuous imaginary time. To do so, we distinguish space- and timelike defects in the lattice-gauge theory. A high free-energy cost of spacelike defects corresponds to a successful “memory experiment” and suppresses the energy splitting among the ground states, while a high free-energy cost of timelike defects corresponds to a successful “stability experiment” and points to a nonzero gap to local excitations.

quantum error correction↗
DOE OSTI2021

Femtosecond control of phonon dynamics near a magnetic order critical point

The spin-phonon interaction in spin density wave (SDW) systems often determines the free energy landscape that drives the evolution of the system. When a passing energy flux, such as photoexcitation, drives a crystalline system far from equilibrium, the resulting lattice displacement generates transient vibrational states. Manipulating intermediate vibrational states in the vicinity of the critical point, where the SDW order parameter changes dramatically, would then allow dynamical control over functional properties. Here we combine double photoexcitation with an X-ray free-electron laser (XFEL) probe to control and detect the lifetime and magnitude of the intermediate vibrational state near the critical point of the SDW in chromium. We apply Landau theory to identify the mechanism of control as a repeated partial quench and sub picosecond recovery of the SDW. Our results showcase the capabilities to influence and monitor quantum states by combining multiple optical photoexcitations with an XFEL probe. They open new avenues for manipulating and researching the behaviour of photoexcited states in charge and spin order systems near the critical point.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗