Spacetime symmetric qubit regularization of the asymptotically free two-dimensional O ( 4 ) model
Not Available
1-dimensional spin chains↗
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Results for “spin qubits”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Extended spin relaxation times of optically addressed vanadium defects in silicon carbide at telecommunication frequencies
Optically interfaced solid-state defects are promising candidates for quantum communication technologies. The ideal defect system would feature bright telecom emission, long-lived spin states, and a scalable material platform, simultaneously. Here, in this study, we use one such system, vanadium (V 4+ ) in silicon carbide, to establish a potential telecom spin-photon interface within a mature semiconductor host. This demonstration of efficient optical spin polarization and readout facilitates all-optical measurements of temperature-dependent spin relaxation times (T 1 ). By using this technique, and lowering the temperature from approximately 2 K to approximately 100 mK, we observe a remarkable 4-orders-of-magnitude increase in spin T 1 across all measured sites, with site-specific values ranging from 57.1 ms to 27.9 s. Furthermore, we identify the underlying relaxation mechanisms, which involve a two-phonon Orbach process, indicating the opportunity for strain tuning to enable qubit operation at higher temperatures. These results position V 4+ in SiC as a prime candidate for scalable quantum nodes in future quantum networks.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Quantum Information for Fusion Energy Sciences (Final Technical Report)
The simulation of plasma dynamics is a critical area of Fusion Energy Sciences (FES) due to it’s usefulness in predicting, controlling, and confining plasmas in the context of potential fusion reactors. The simulation of plasmas is a computationally difficult problem in both classical and quantum physics, motivating investigation into the potential of quantum computers to simulate these systems. This project took several concrete steps towards this goal by developing tools for improving the control, characterization, and calibration of quantum gates on a superconducting quantum computer, developing error suppression and mitigation tools to reduce errors on the quantum computer, and utilizing these advancements to simulate reduced models of plasma dynamics on the quantum computer. In order to efficiently simulate plasma physics, an optimal control method which synthesizes, directly at the pulse level, any quantum gate on qubit and qutrit systems was developed. Using four superconducting transmon quantum processors at Rigetti and LLNL, it was demonstrated that any arbitrary quantum gate on qubits and qutrits could be implemented with high fidelity, leading to a significantly reduced length of a gate sequence. A problem of interest in FES is the nonlinear optical process of laser pulse compression within a plasma. Since quantum physics is linear, simulating nonlinear operations is not naturally feasible on a quantum computer, however it is possible to simulated a quantized version of the nonlinear process. A quantization approach to convert nonlinear wave-wave interaction problems to Hamiltonian simulation problems was developed and demonstrated using two qubits on a Rigetti device. In this experiment, a number of error suppression and mitigation techniques were investigated to determine how best to utilize the finite quantum resources. This study provides an example of how plasma problems may be solved on near-term, noisy quantum computing platforms and identified a promising set of techniques. Building on the insights of these experiments, the investigation turned to linear electron-plasma wave physics. A connection was identified between a local one-dimensional lattice spin model and linear wave phenomena, allowing a plasma physics problem to be efficiently mapped to the quantum computer. In this framework, reflection and transmission of plasma waves at a sharp boundary was studied, as well as the propagation of waves through an inhomogeneous plasma medium. In addition to the suite of error suppression and mitigation techniques developed, this experiment introduced the use of a digital-analog gate scheme designed to efficiently simulate the plasma Hamiltonian. With hardware available at the conclusion of the project, simulation at the scale of 9 qubits and 15 timesteps (60 entangling layers) was achieved.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Hysteretic Responses of Skyrmion Lattices to Electric Fields in Magnetoelectric Cu 2 OSeO 3
Electric field control of topologically nontrivial magnetic textures, such as skyrmions, provides a paradigm shift for future spintronics beyond current silicon-based technology. While significant progress has been made by X-ray and neutron scattering studies, direct observation of such nanoscale spin structures and their dynamics driven by external electric fields remains a challenge to understand underlying mechanisms and harness functionalities. Here, using Lorentz transmission electron microscopy combined with in situ electric and magnetic fields at liquid helium temperatures, we report the crystallographic-orientation dependent skyrmion responses to electric fields in thin slabs of magnetoelectric Cu 2 OSeO 3 . We show electric fields not only stabilize the hexagonally packed skyrmion lattices in the entire sample in a hysteretic manner but also induce the rotation of their reciprocal vector discretely by 30°. Furthermore, the nonvolatile and energy-efficient skyrmion-lattice control by electric fields demonstrated in this work provides an important foundation for designing skyrmion-based qubits and memory devices.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Quantum guidelines for solid-state spin defects
Defects with associated electron and nuclear spins in solid-state materials have a long history relevant to quantum information science going back to the first spin echo experiments with silicon dopants in the 1950s. Since the turn of the century, the field has rapidly spread to a vast array of defects and host crystals applicable to quantum communication, sensing, and computing. From simple spin resonance to long-distance remote entanglement, the complexity of working with spin defects is fast advancing, and requires an in-depth understanding of their spin, optical, charge, and material properties in this modern context. This is especially critical for discovering new relevant systems dedicated to specific quantum applications. In this review, we therefore expand upon all the key components with an emphasis on the properties of defects and the host material,on engineering opportunities and other pathways for improvement. Finally, this review aims to be as defect and material agnostic as possible, with some emphasis on optical emitters,providing a broad guideline for the field of solid-state spin defects for quantum information.
36 MATERIALS SCIENCE↗
Magic Diamond: Covalent Bond Formation of Melamine and Other Amines on Nanodiamond Surfaces
High-temperature, high-pressure (HPHT) nanodiamond (ND) hosts nitrogen-vacancy (NV) centers, solid-state qubits that enable room-temperature quantum sensing by all-optical magnetometry, electrometry, and thermometry. However, the covalent surface functionalization of nanoscale diamond remains largely limited to carboxylate-based chemistries. Amine termination is particularly attractive because theoretical studies predict suppression of midgap states and extended electron-spin coherence times. Recently, chemical activation of alcohol-terminated NDs to alkyl bromides (ND-Br) using SOBr2 has enabled nucleophilic substitution through a carbocation intermediate, allowing formation of simple amine terminations. Here, we evaluate whether sterically demanding amines can form covalent diamond−nitrogen bonds on ND-Br surfaces. ND-Br was reacted with branched, linear, and cyclic amines, including polyethylenimine, diethylenetriamine, and melamine. X-ray spectroscopies were used to confirm successful and to probe the resulting electronic structure at the diamond−amine interface. These results expand the chemical toolbox for tuning diamond surface dipoles and electron affinity, providing new pathways for engineering nanodiamond surfaces for quantum sensing and photocatalysis applications.
Amines↗
Quantum Quench Dynamics–Crossover Phenomena in Nonequilibrium Correlated Quantum Systems (Final Technical Report)
In this project we have developed analytical and numerical tools to study the interplay between interactions, dimensionality, fluctuations and disorder in quantum impurity systems. We have studied the transient dynamics following a quench, i.e. the sudden change in a control variable of the model Hamiltonian, which offers a unique way to examine the system’s spatial, temporal and energetic structure. Specifically, we have investigated how crossover scales, i.e. given by Kondo couplings, are affected by disorder. We have addressed a wide range of phenomena, such as the effects of static disorder on dynamical screening of magnetic impurities, and the influence of a fully time-fluctuating bath environment on the dephasing of system qubits. We have found that many of these systems exhibit fascinating counterintuitive behavior, such as e.g. the possibility of asymptotic unitary time evolution in specifically conditioned system-bath Hamiltonians. From a technical point of view, we have developed a supersymmetric formalism to analyze scaling functions of disordered quantum impurity spin chains, we generalized the strong-coupling real-space renormalization group method to probe the quench dynamics of higher-dimensional quantum impurity systems, and we devised a master equation approach that included the effects of a fully fluctuating environment. This way, we have addressed a very broad spectrum of transient phenomena in quantum impurity systems, with disorder ranging from the quenched to the annealed limit.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Optical properties of a diamond NV color center from capped embedded multiconfigurational correlated wavefunction theory
Diamond defects are among the most promising qubits. Modeling their properties through accurate quantum mechanical simulations can further their development into robust units of information. We use the recently developed capped density functional embedding theory (capped-DFET) with the multiconfigurational n-electron valence second-order perturbation theory to characterize the electronic excitation energies for different spin manifolds of the well-characterized negatively charged substitutional N defect adjacent to a vacancy (V C ) in diamond (N C V C − ). We successfully reproduce vertical excitation energies for both triplet and singlet states of N C V C − with errors < 0.1 eV. Unlike other embedding methods, capped-DFET exhibits robust predictions that are approximately independent of the embedded cluster size: it only requires a cluster to contain the defect atoms and their nearest neighbors (as small as a 40-atom capped cluster). Furthermore, our method is free from slowly converging Coulomb interactions between charged defects, and thus also only weakly dependent on supercell size.
Chemistry↗
Improving Schrödinger Equation Implementations with Gray Code for Adiabatic Quantum Computers
We reformulate the continuous-space Schrödinger equation in terms of spin Hamiltonians. For the kinetic energy operator, the critical concept facilitating the reduction in model complexity is the idea of position encoding. A binary encoding of position produces a spin-1/2 Heisenberg-like model and yields exponential improvement in space complexity when compared to classical computing. Encoding with a binary reflected Gray code (BRGC), and a Hamming-distance-2 Gray code (H2GC) reduces the model complexity down to the 𝑋𝑍 and transverse Ising model, respectively. For 𝐴 qubits BRGC yields 2 𝐴 positions and is reduced to its 2-local form with O(𝐴) ancillary qubits. H2GC yields 2 𝐴/2+1 positions with O(𝐴 2 ) three-local penalty terms. We also identify the bijective mapping between diagonal unitaries and the Walsh series, producing the mapping of any real potential to a series of 𝑘 -local Ising models through the fast Walsh transform. Finally, in a finite volume, we provide some numerical evidence to support the claim that the total time needed for adiabatic evolution is protected by the infrared cutoff of the system. As a result, initial state preparation from a free-field wave function to an interacting system is expected to exhibit polynomial time complexity with volume and constant scaling with respect to lattice discretization for all encodings. For H2GC, if the evolution starts with the transverse Hamiltonian due to hardware restrictions, then penalties are dynamically introduced such that the low-lying spectrum reproduces the energy levels of the Laplacian. The adiabatic evolution of the penalty Hamiltonian is therefore sensitive to the ultraviolet scale. It is expected to exhibit polynomial time complexity with lattice discretization, or exponential time complexity with respect to the number of qubits given a fixed volume.
97 MATHEMATICS AND COMPUTING↗
Constant-depth circuits for dynamic simulations of materials on quantum computers
Abstract Dynamic simulation of materials is a promising application for near-term quantum computers. Current algorithms for Hamiltonian simulation, however, produce circuits that grow in depth with increasing simulation time, limiting feasible simulations to short-time dynamics. Here, we present a method for generating circuits that are constant in depth with increasing simulation time for a specific subset of one-dimensional (1D) materials Hamiltonians, thereby enabling simulations out to arbitrarily long times. Furthermore, by removing the effective limit on the number of feasibly simulatable time-steps, the constant-depth circuits enable Trotter error to be made negligibly small by allowing simulations to be broken into arbitrarily many time-steps. For an N -spin system, the constant-depth circuit contains only $\mathcal {O}(N^{2})$ O ( N 2 ) CNOT gates. Such compact circuits enable us to successfully execute long-time dynamic simulation of ubiquitous models, such as the transverse field Ising and XY models, on current quantum hardware for systems of up to 5 qubits without the need for complex error mitigation techniques. Aside from enabling long-time dynamic simulations with minimal Trotter error for a specific subset of 1D Hamiltonians, our constant-depth circuits can advance materials simulations on quantum computers more broadly in a number of indirect ways.
Materials simulation↗
Rephasing spectral diffusion in time-bin spin-spin entanglement protocols
Generating high-fidelity spin-spin entanglement is an essential task of quantum repeater networks for the distribution of quantum information across long distances. Solid-state-based spin-photon interfaces are promising candidates to realize nodes of a quantum network, but are often limited by spectral diffusion of the optical transition, which results in phase errors on the entangled states. Here, we introduce a method to correct phase errors from quasi-static frequency fluctuations after the entangled state is generated, by shelving the emitters in the excited state to refocus the unknown phase. For quasi-static frequency fluctuations, the fidelity is determined only by the lifetime of the excited state used for shelving, making it particularly suitable for systems with a long-lived shelving state with correlated spectral diffusion. Such a shelving state may be found in Kramers doublet systems such as rare-earth emitters and color centers in Si or SiC interfaced with nanophotonic cavities with a strongly frequency-dependent Purcell enhancement. Furthermore, the protocol can be used to generate high-fidelity entangled spin pairs without reducing the rate of entanglement generation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Probing the Kitaev honeycomb model on a neutral-atom quantum computer
Quantum simulations of many-body systems are among the most promising applications of quantum computers. In particular, models based on strongly correlated fermions are central to our understanding of quantum chemistry and materials problems, and can lead to exotic, topological phases of matter. However, owing to the non-local nature of fermions, such models are challenging to simulate with qubit devices. Here we realize a digital quantum simulation architecture for two-dimensional fermionic systems based on reconfigurable atom arrays. We utilize a fermion-to-qubit mapping based on Kitaev’s model on a honeycomb lattice, in which fermionic statistics are encoded using long-range entangled states. We prepare these states efficiently using measurement and feedforward, realize subsequent fermionic evolution through Floquet engineering with tunable entangling gates interspersed with atom rearrangement, and improve results with built-in error detection. Leveraging this fermion description of the Kitaev spin model, we efficiently prepare topological states across its complex phase diagram and verify the non-Abelian spin-liquid phase by evaluating an odd Chern number. We further explore this two-dimensional fermion system by realizing tunable dynamics and directly probing fermion exchange statistics. Finally, we simulate strong interactions and study the dynamics of the Fermi–Hubbard model on a square lattice. These results pave the way for digital quantum simulations of complex fermionic systems for materials science, chemistry and high-energy physics.
atomic and molecular physics↗
Qudit Designs and Where to Find Them
Unitary t-designs are some of the most versatile tools in quantum information theory. Their applications range from randomized benchmarking and shadow tomography, to more fundamental ones such as emulating quantum chaos and establishing exponential separations between classical and quantum query complexity. While unitary designs originating from a group structure, such as the Clifford group, have proven to be incredibly useful for qubit systems, unfortunately, this is no longer true for qudits. In fact, the classification of finite-group representations rules out the existence of unitary 2-designs for arbitrary qudit dimensions. This severely limits the applicability of standard quantum information primitives when it comes to qudit systems. We overcome these limitations with a three-fold contribution. First, we introduce a general technique to construct families of weighted state t-designs in arbitrary qudit dimensions. These weighted state-designs generalize classical shadow tomography protocol from qubits to qudits. Second, we introduce a Clifford character RB that allows us to benchmark the qudit Clifford group in any dimension, including non-prime-power dimensions. And third, we establish bounds on the quantum circuit complexity of generating approximate unitary-designs from native gates in existing quantum hardware such as high-spin and cavity-QED qudits. Our work further highlights the analogy between spin and optical coherent states by proving that spin-GKP codewords form a state 2-design while spin coherent states do not; in direct analogy with the optical case. This work is structured as a pedagogical and self-contained introduction to unitary designs and their applications to qudit systems.
Anand, Namit [NASA, Ames; Unlisted, US] (ORCID:000↗
From Asymptotic Freedom to θ Vacua: Qubit Embeddings of the O(3) Nonlinear σ Model
Not Available
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Variational quantum simulation of the critical Ising model with symmetry averaging
Here we investigate the use of deep multiscale entanglement renormalization ansatz (DMERA) circuits as a variational ansatz. We use the exactly solvable one-dimensional critical transverse-field Ising model as a test bed. Numerically exact simulation of the quantum circuit ansatz can in this case be carried out to hundreds of qubits by exploiting efficient classical algorithms for simulating matchgate circuits. We find that, for this system, the DMERA strongly outperforms a standard quantum approximate optimization algorithm (QAOA)–style ansatz, and that a major source of systematic error in correlation functions approximated using the DMERA is the breaking of the translational and Kramers-Wannier symmetries of the transverse-field Ising model. We are able to reduce this error by up to four orders of magnitude by symmetry averaging, without incurring additional cost in qubits or circuit depth. Here, we propose that this technique for mitigating systematic error could be applied to noisy intermediate-scale quantum (NISQ) simulations of physical systems with other symmetries.
1-dimensional spin chains↗
Mechanical Control of a Single Nuclear Spin
Not Available
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Field programmable spin arrays for scalable quantum repeaters
The large scale control over thousands of quantum emitters desired by quantum network technology is limited by the power consumption and cross-talk inherent in current microwave techniques. Here we propose a quantum repeater architecture based on densely-packed diamond color centers (CCs) in a programmable electrode array, with quantum gates driven by electric or strain fields. This ‘field programmable spin array’ (FPSA) enables high-speed spin control of individual CCs with low cross-talk and power dissipation. Integrated in a slow-light waveguide for efficient optical coupling, the FPSA serves as a quantum interface for optically-mediated entanglement. We evaluate the performance of the FPSA architecture in comparison to a routing-tree design and show an increased entanglement generation rate scaling into the thousand-qubit regime. Our results enable high fidelity control of dense quantum emitter arrays for scalable networking.
42 ENGINEERING↗
Searching for axion dark matter with array-scalable single magnon detectors
We introduce an array-scalable, magnon-based detector to search for the spin-dependent interactions of electron-coupled axion dark matter with mass in the 1−100 μeV range. These axions can excite single magnons in magnetic targets, such as yttrium iron garnet (YIG) spheres, which are subsequently sensed by the detector. In our concept, this sensing is implemented by coupling the magnons in the YIG spheres to magnetic-field-resilient single-electron charge-qubits, whose state is then interrogated with a quantum nondemolition measurement. Using standard superconducting fabrication techniques, it is possible to integrate many YIG sphere-qubit sensors, forming a large detector array. We outline the detector design and operation for our concept, and determine its sensitivity to axion dark matter. We find that using available technology can already exceed the sensitivity of previous ferromagnetic haloscopes, and further improvements in performance would search for electron-coupled axion dark matter in unexplored parameter space.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗