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At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Reaching quantum critical point by adding nonmagnetic disorder in single crystals of superconductor (Ca 𝑥 ⁢Sr 1−𝑥 ) 3 ⁢Rh 4 ⁢Sn 13

The Remeika series superconductor, (Ca 𝑥 ⁢Sr 1−𝑥 ) 3 ⁢Rh 4 ⁢Sn 13 , shows a rare nonmagnetic quantum critical point (QCP) associated with the continuous charge-density wave (CDW) and structural transition under the “dome” of superconductivity achieved by tuning composition and applying pressure. Here, we use a nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation to suppress the CDW and drive the system to and even beyond the QCP. This conclusion is based on a clear evolution of temperature-dependent resistivity, 𝜌⁡(𝑇), from the Fermi liquid to the non-Fermi liquid regime with increasing amount of disorder. Starting on the CDW side, below the suggested QCP concentration of 𝑥 𝑐 =0.9, added disorder resulted in a progressively larger linear term and a reduced quadratic term in 𝜌⁡(𝑇). Nearly perfect 𝑇−linear dependence is observed at the dose at which long-range CDW order is suppressed to 𝑇=0, consistent with the expectations. We refine the QCP location in this system and place it in the interval between 𝑥=0.75 and 0.85. Our results strongly support the concept that the disorder can tune the system to the quantum critical regime and even beyond. It follows from the argument by Imry and Ma that any ordered phase is unstable toward quenched disorder. Introduced in a controlled way, this disorder becomes a nonthermal tuning parameter likely applicable to a variety of different systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Scattering in the Ising model with the quantum Lanczos algorithm *

Abstract Time evolution and scattering simulation in phenomenological models are of great interest for testing and validating the potential for near-term quantum computers to simulate quantum field theories. Here, we simulate one-particle propagation and two-particle scattering in the one-dimensional transverse Ising model for 3 and 4 spatial sites with periodic boundary conditions on a quantum computer. We use the quantum Lanczos algorithm to obtain all energy levels and corresponding eigenstates of the system. We simplify the quantum computation by taking advantage of the symmetries of the system. These results enable us to compute one- and two-particle transition amplitudes, particle numbers for spatial sites, and the transverse magnetization as functions of time. The quantum circuits were executed on various IBM Q superconducting hardware. The experimental results are in very good agreement with the values obtained using exact diagonalization.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Quantum-enhanced phase imaging without coincidence counting

Quantitative phase imaging provides a way to image transparent objects, such as biological cells, and measure their thickness. We report on a phase-imaging method that achieves twice the phase shift and approximately 1.7 times the spatial resolution of an equivalent spatially and temporally coherent classical quantitative phase-imaging system by using quantum interference between successive spontaneous parametric downconversion events in a nonlinear crystal. Furthermore, our method is approximately 1000 times faster than imaging the parametric downconversion photons in coincidence, which requires measurement times on the order of tens of hours. Our method may be useful for imaging sensitive transparent objects that require low illumination intensities at near-infrared and longer illumination wavelengths, such as photosensitive biological samples.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Strong parametric dispersive shifts in a statically decoupled two-qubit cavity QED system

Qubits in cavity quantum electrodynamic (QED) architectures are often operated in the dispersive regime, in which the operating frequency of the cavity depends on the energy state of the qubit, and vice versa. The ability to tune these dispersive shifts provides additional options for performing either quantum measurements or logical manipulations. Here we couple two transmon qubits to a lumped-element cavity through a shared superconducting quantum interference device (SQUID). In this work, our design balances the mutual capacitive and inductive circuit components so that both qubits are statically decoupled from the cavity with low flux sensitivity, offering protection from decoherence processes. Parametric driving of the SQUID flux enables independent, dynamical tuning of each qubit’s interaction with the cavity. As a practical demonstration, we perform pulsed parametric dispersive readout of both qubits. The dispersive frequency shifts of the cavity mode follow the theoretically expected magnitude and sign. This parametric approach creates an extensible, tunable cavity QED framework with various future applications, such as entanglement and error correction via multi-qubit parity readout, state and entanglement stabilization, and parametric logical gates.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2006

Is Q for Quantum? From Quantum Mechanics to Formation of the Solar System

The realization in 1985 that fullerenes exist in nature [1] as a third form of carbon-carbon clustering, continues to inspire new areas of research. In particular, the study of closed-cage endohedral fullerenes [2-6] is of scientific interest because of its potential application in a number of promising fields from medical imaging to astrophysics. One of these is to provide a possible chronometer for studying the age and origin of certain astromaterials in the solar system. Fullerenes are closed carbon cages that are fundamentally related to a long-standing debate over the "Q-Phase" origin of planetary noble gases in carbonaceous chondrites [7]. Although Q-phase has been identified as the carrier of planetary noble gases [8- 10], its physical nature has not been explained. Our limited understanding of it is based primarily on the laboratory chemical processing which it survives as well as the fact that it must have been widely distributed in the solar nebula [11]. Yet as important as it might be while preoccupying some 30 years of research, the question of what actually is Q-phase remains unresolved.

Wilson, T. L.↗
DOE OSTI2020

Quantum random number generator

A system and method are provided to yield a QRNG based on homodyne detection of quantum noise (e.g., vacuum noise measured as shot noise) generated from a local oscillator, such as an LED. In one embodiment, a QRNG may be provided that is adjustable based on a control input to produce a random output that can be translated to one or more random data bits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

VTS Dynamic Model and Experimental Validation for Vibration Suppression

High Q-factor superconducting radio-frequency (SRF) cavities are extremely sensitive to mechanical vibrations, which can cause an uncontrolled shift of the electromagnetic resonance frequency, with detrimental effects on the cavity performance. To avoid this phenomenon (i.e. microphonics) the dynamic behavior of the assembly must be studied, to design vibration suppression systems. In this paper, the numerical model of the Vertical Test Stand (VTS) insert adopted at the Fermi National Accelerator Laboratory for cold tests was studied, in the framework of the experimental characterization of Dark SRF cavities conducted by the SQMS (Superconducting Quantum Materials and Systems) center. Due to the complexity of the assembly, experimental activity is of utmost importance to validate the model. Thus, vibration testing was performed on the actual system, and a good correlation between numerical and experimental results was found. Additionally, two different setups were compared, with and without implementing a preliminary passive vibration suppression system, to assess its effectiveness in reducing the microphonics phenomenon. The obtained results allowed for the design of an improved isolation system, which will be the subject of future experimental testing.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Seamless High-Q Microwave Cavities for Multimode Circuit Quantum Electrodynamics

Multimode cavity quantum electrodynamics ---where a two-level system interacts simultaneously with many cavity modes---provides a versatile framework for quantum information processing and quantum optics. Due to the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of $2$ ms and cooperativities of $0.5-1.5\times10^9$ across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Design of axion and axion dark matter searches based on ultra high Q SRF cavities

The Superconducting Quantum Materials and Systems center is developing searches for dark photons, axions and ALPs with the goal of improving upon the current state-of-the-art sensitivity. These efforts leverage on Fermi National Accelerator expertise on ultra-high quality factor superconducting radio frequency cavities combined with the center research on quantum technology. Here we focus on multiple axion searches that utilize ~1E10 quality factor superconducting radio frequency cavities and their resonant modes to enhance the production and/or detection of axions in the cavity volume. In addition, we present preliminary results of single-mode and multi-mode nonlinearity measurements that were carried out as part of an experimental feasibility study to gain insight on the behavior of the ultra-high quality factor resonators and the experimental RF system in the regime relevant for axion searches.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Absence of Barren Plateaus and Scaling of Gradients in the Energy Optimization of Isometric Tensor Network States

Abstract Vanishing gradients can pose substantial obstacles for high-dimensional optimization problems. Here we consider energy minimization problems for quantum many-body systems with extensive Hamiltonians and finite-range interactions, which can be studied on classical computers or in the form of variational quantum eigensolvers on quantum computers. Barren plateaus correspond to scenarios where the average amplitude of the energy gradient decreases exponentially with increasing system size. This occurs, for example, for quantum neural networks and for brickwall quantum circuits when the depth increases polynomially in the system size. Here we prove that the variational optimization problems for matrix product states, tree tensor networks, and the multiscale entanglement renormalization ansatz are free of barren plateaus. The derived scaling properties for the gradient variance provide an analytical guarantee for the trainability of randomly initialized tensor network states (TNS) and motivate certain initialization schemes. In a suitable representation, unitary tensors that parametrize the TNS are sampled according to the uniform Haar measure. We employ a Riemannian formulation of the gradient based optimizations which simplifies the analytical evaluation.

Barthel, Thomas↗
DOE OSTI2022

Beyond quantum cluster theories: multiscale approaches for strongly correlated systems

The degrees of freedom that confer to strongly correlated systems their many intriguing properties also render them fairly intractable through typical perturbative treatments. For this reason, the mechanisms responsible for their technologically promising properties remain mostly elusive. Computational approaches have played a major role in efforts to fill this void. In particular, dynamical mean field theory and its cluster extension, the dynamical cluster approximation have allowed significant progress. However, despite all the insightful results of these embedding schemes, computational constraints, such as the minus sign problem in quantum Monte Carlo (QMC), and the exponential growth of the Hilbert space in exact diagonalization (ED) methods, still limit the length scale within which correlations can be treated exactly in the formalism. A recent advance aiming to overcome these difficulties is the development of multiscale many body approaches whereby this challenge is addressed by introducing an intermediate length scale between the short length scale where correlations are treated exactly using a cluster solver such QMC or ED, and the long length scale where correlations are treated in a mean field manner. At this intermediate length scale correlations can be treated perturbatively. This is the essence of multiscale many-body methods. Furthermore, we will review various implementations of these multiscale many-body approaches, the results they have produced, and the outstanding challenges that should be addressed for further advances.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Quantum noise and the threshold of hearing

It is argued that the sensitivity of the ear reaches a limit imposed by the uncertainty principle. This is possible only if the receptor cell holds the detector elements in a special nonequilibrium state which has the same noise characteristics as a ground (T = 0 K) state. To accomplish this 'active cooling' the molecular dynamics of the system must maintain quantum mechanical coherence over the time scale of the measurement.

Bialek, W.↗
DOE OSTI2024

Investigation of cosmic ray impact on transmon qubits with different materials through fast decay detection at Fermilab’s SQMS laboratory

Noise sources affecting superconducting qubits, such as cosmic rays and ambient gamma radiation, have garnered attention for their potential impact. These radiations deposit energy in the qubit's substrate, generating high-energy phonons that break Cooper pairs, leading to the formation of quasi-particles. When these quasi-particles tunnel across Josephson junctions, they induce qubit de-excitation, causing relaxation errors. In this study, we employ a fast feedback mechanism for performing qubit reset to detect decay events with high time resolution. This capability along with frequency multiplexed readout allows us to explore error correlations across time and space. Transmon qubits, manufactured within the Superconducting Quantum Materials and Systems (SQMS) center [1], are investigated at the above-ground lab. We study the impact of cosmic rays on qubits with different encapsulations, geometries, and locations on the same or different chips. We present preliminary findings and discuss the implications for the performance of contemporary quantum hardware.

Roy, Tanay↗
DOE OSTI2022

Advanced architectures for high-performance quantum networking

As practical quantum networks prepare to serve an ever-expanding number of nodes, there has grown a need for advanced auxiliary classical systems that support the quantum protocols and maintain compatibility with the existing fiber-optic infrastructure. We propose and demonstrate a quantum local area network design that addresses current deployment limitations in timing and security in a scalable fashion using commercial off-the-shelf components. First, we employ White Rabbit switches to synchronize three remote nodes with ultra-low timing jitter, significantly increasing the fidelities of the distributed entangled states over previous work with Global Positioning System clocks. Second, using a parallel quantum key distribution channel, we secure the classical communications needed for instrument control and data management. Therefore, the conventional network that manages our entanglement network is secured using keys generated via an underlying quantum key distribution layer, preserving the integrity of the supporting systems and the relevant data in a future-proof fashion.

97 MATHEMATICS AND COMPUTING↗