Semiconductor spin qubits

Abstract

The spin degree of freedom of an electron or a nucleus is one of the most basic properties of nature and functions as an excellent qubit, as it provides a natural two-level system that is insensitive to electric fields, leading to long quantum coherence times. This coherence survives when the spin is isolated and controlled within nanometer-scale, lithographically fabricated semiconductor devices, enabling the existing microelectronics industry to help advance spin qubits into a scalable technology. Driven by the burgeoning field of quantum information science, worldwide efforts have developed semiconductor spin qubits to the point where quantum state preparation, multiqubit coherent control, and single-shot quantum measurement are now routine. The small size, high density, long coherence times, and available industrial infrastructure of these qubits provide a highly competitive candidate for scalable solid-state quantum information processing. We review the physics of semiconductor spin qubits, focusing not only on the early achievements of spin initialization, control, and readout in GaAs quantum dots, but also on recent advances in Si and Ge spin qubits, including improved charge control and readout, coupling to other quantum degrees of freedom, and scaling to larger system sizes. We begin by introducing the four major types of spin qubits: single spin qubits, donor spin qubits, singlet-triplet spin qubits, and exchange-only spin qubits. We then review the mesoscopic physics of quantum dots, including single-electron charging, valleys, and spin-orbit coupling. We next give a comprehensive overview of the physics of exchange interactions, a crucial resource for single-and two-qubit control in spin qubits. The bulk of this review is centered on the presentation of results from each major spin qubit type, the present limits of fidelity, and a brief overview of alternative spin qubit platforms. We then give a physical description of the impact of noise on semiconductor spin qubits, aided in large part by an introduction to the filter function formalism. Lastly, we review recent efforts to hybridize spin qubits with superconducting systems, including charge-photon coupling, spin-photon coupling, and long-range cavity-mediated spin-spin interactions. Cavity-based readout approaches are also discussed. This review is intended to give an appreciation for the future prospects of semiconductor spin qubits, while highlighting the key advances in mesoscopic physics over the past two decades that underlie the operation of modern quantum-dot and donor-spin qubits. CONTENTS1. Spin transport, spin SWAPs, and spin-CTAP 24 2. Superexchange 25 3. Capacitive and electric dipole-dipole couplings 26 4. Cavity QED 26 V. Quantum gates and quantum circuits 26 A. Loss-DiVincenzo single spin qubits 27 1. Initialization and readout 27 2. Single-qubit gates 28 3. Two-qubit gates 29 4. Limits of fidelity -randomized benchmarking 30 B. Donor spin qubits 31 1. Donor electron spin initialization and readout 31 2. Donor electron spin single-qu...

Spin–orbit interaction enabled high-fidelity two-qubit gates

“…We should emphasize such parametrization is only valid in the setup considered here, where the kinetic effect (i.e. interdot tunneling) is the dominant contribution to the exchange [8]. Finally, we note that these parameters are easily accessibile to experimental control by the changing the magnetic field angle and the effective SOI coupling strength of the device.…”

Quantum Vibronic Effects on the Excitation Energies of the Nitrogen-Vacancy Center in Diamond

“…b Extrapolated to the infinite supercell limit based on the calculations on C 62 N and C 214 N supercells (see Table S3). c Not directly measured; obtained from the measured ZPL/VEE's of 3 A 2 → 3 E and 1 A 1 → 1 E and the energy difference between states 3 E and 1 A 1 (see ref 21). order of a hundred millielectronvolts) due to quantum vibronic effects of the ground state.…”

“…Spin defects in semiconductors have the potential to allow the realization of quantum technologies working near room temperature . Various applications have been suggested in the literature, including quantum sensing, , quantum communication, and quantum computing. , However, despite rapid experimental and theoretical progress in the past decade, challenges remain in controlling and increasing the coherence time of spin qubits, which is ultimately limited by quantum vibronic effects (electron–phonon interactions) .…”

Optically Driven Both Classical and Quantum Unary, Binary, and Ternary Logic Gates on Co-Decorated Graphene Nanoflakes

“…A crucial issue of quantum information theory is the quantification of the similarity between two quantum states. , Although the role of interaction mechanisms between superposition states in quantum computational speedup is not yet clear, these mechanisms indubitably play a crucial role in the development of quantum computing, particularly in various quantum-spin systems. − In the past couple of years, efforts have been vigorously made to delve into ultrafast spin operations on multiqubits and their potential contributions to quantum computations. − In order to build actual logic processing units, one must not only discover and functionalize spin-operations on quantum dots (QDs) but also integrate them into magnetic heterostructures. In this respect many mechanisms and a large variety of systems have been proposed. − Among them, molecular systems are expected to miniaturize the envisaged magnetic-logic elements, − since they can accommodate Boolean logic processes, while some logic operations have been proposed on the basis of realistic or even synthesized quantum dots. − Moreover, the development of compact out-of-plane focusing grating couplers for integration with magnetoresistive random access memory technology makes the all-optical spin manipulation even more suitable in spintronics devices .…”