Electric Dipole Spin Resonance Research Articles

Measurement of Enhanced Spin-Orbit Coupling Strength for Donor-Bound Electron Spins in Silicon.

While traditionally considered a deleterious effect in quantum dot spin qubits, the spin-orbit interaction is recently being revisited as it allows for rapid coherent control by on-chip AC electric fields. For electrons in bulk silicon, spin-orbit coupling (SOC) is intrinsically weak, however, it can be enhanced at surfaces and interfaces, or through atomic placement. Here it is showed that the strength of the spin-orbit coupling can be locally enhanced by more than two orders of magnitude in the manybody wave functions of multi-donor quantum dots compared to a single donor, reaching strengths so far only reported for holes or two-donor system with certain symmetry. These findings may provide a pathway toward all-electrical control of donor-bound spins in silicon using electric dipole spin resonance (EDSR).

Electrical manipulation of the spins in phosphorene double quantum dots

We investigate electric dipole spin resonance (EDSR) induced by an oscillating electric field within a system of double quantum dots formed electrostatically in monolayer phosphorene. Apart from the observed anisotropy of effective masses, phosphorene has been predicted to exhibit anisotropic spin-orbit coupling. Here, we examine a system consisting of two electrons confined in double quantum dots. A single-band effective Hamiltonian together with the configuration interaction theory is implemented to simulate the time evolution of the ground state. We examine spin flips resulting from singlet-triplet transitions driven by external AC electric fields, both near and away from the Pauli blockade regime, revealing fast sub-nanosecond transition times. Furthermore, we analyze the impact of anisotropy by comparing dots arranged along a different crystal axis. The sub-harmonic multi-photon transitions and Landau-Zener-Stückelberg-Majorana transitions are discussed. We show modulation of spin-like and charge-like characteristics of the qubit through potential detuning.

Electric field dependence of spin qubit in a Si-MOS quantum dot

Abstract Valley, the intrinsic feature of silicon, is an inescapable subject in silicon-based quantum computing. At the spin–valley hotspot, both Rabi frequency and state relaxation rate are significantly enhanced. With protection against charge noise, the valley degree of freedom is also conceived to encode a qubit to realize noise-resistant quantum computing. Here, based on the spin qubit composed of one or three electrons, we characterize the intrinsic properties of valley in an isotopically enriched silicon quantum dot (QD) device. For one-electron qubit, we measure two electric-dipole spin resonance (EDSR) signals which are attributed to partial occupation of two valley states. The resonance frequencies of two EDSR signals have opposite electric field dependences. Moreover, we characterize the electric field dependence of the upper valley state based on three-electron qubit experiments. The difference of electric field dependences of the two valleys is 52.02 MHz/V, which is beneficial for tuning qubit frequency to meet different experimental requirements. As an extension of electrical control spin qubits, the opposite electric field dependence is crucial for qubit addressability, individual single-qubit control and two-qubit gate approaches in scalable quantum computing.

Analysis and 3D TCAD simulations of single-qubit control in an industrially-compatible FD-SOI device

In this study, 3D simulations are introduced to analyze electric-dipole spin resonance (EDSR) for a spin qubit defined in a 28nm-node Ultra-Thin Body and Buried oxide (UTBB) Fully-Depleted Silicon-On-Insulator (FD-SOI) device operated at cryogenic temperatures. The device under consideration is designed to be compatible with STMicroelectronics’ standard fabrication techniques. The simulations predict the experimental and device parameters (e.g. drive amplitude, leakage, and Rabi frequency) required to make EDSR a viable means of qubit control before the device is fabricated. This work highlights how 3D TCAD tools which can simulate quantum-mechanical effects can help steer the design of quantum devices.

Controllable single-spin evolution at subharmonics of electric dipole spin resonance enhanced by four-level Landau-Zener-Stückelberg-Majorana interference

Controllable single-spin evolution at subharmonics of electric dipole spin resonance enhanced by four-level Landau-Zener-Stückelberg-Majorana interference

Dynamical nuclear spin polarization in a quantum dot with an electron spin driven by electric dipole spin resonance

Dynamical nuclear spin polarization in a quantum dot with an electron spin driven by electric dipole spin resonance

Photo-assisted spin transport in double quantum dots with spin–orbit interaction

We investigate the effect of spin–orbit interaction on the intra- and interdot particle dynamics of a double quantum dot (QD) under ac electric fields. The former is modeled as an effective ac magnetic field that produces electric-dipole spin resonance transitions, while the latter is introduced via spin-flip tunneling amplitudes. We observe the appearance of non-trivial spin-polarized dark states (DSs), arising from an ac-induced interference between photo-assisted spin-conserving and spin-flip tunneling processes. These DSs can be employed to precisely measure the spin–orbit coupling in QD systems. Furthermore, we show that the interplay between photo-assisted transitions and spin-flip tunneling enables the system to operate as a highly tunable spin filter. Finally, we investigate the operation of the system as a resonant flopping-mode qubit for arbitrary ac voltage amplitudes, allowing for high tunability and enhanced qubit control possibilities.

Light-hole gate-defined spin-orbit qubit

The selective confinement of light-holes (LHs) is demonstrated by introducing a low-dimensional system consisting of highly tensile-strained Ge quantum well enabling the design of an ultrafast gate-defined spin qubit under the electric dipole spin resonance. The qubit size-dependent $g$-factor and dipole moment are mapped, and the parameters inducing their modulation are discussed. It is found that the LH qubit dipole moment is 2 to 3 orders of magnitude higher than that of the canonical heavy-hole qubit. This behavior originates from the significant spin splitting resulting from the combined action of large cubic and linear Rashba spin-orbit interactions that are peculiar to LHs. The qubit relaxation rate is also affected by the strong spin-orbit interaction and follows typically a $B^7$ behavior. The proposed all-group IV, direct bandgap LH qubit provides an effective platform for a scalable qubit-optical photon interface sought-after for long-range entanglement distribution and quantum networks.

Acceptor-based qubit in silicon with tunable strain

Long coherence time and compatibility with semiconductor fabrication make spin qubits in silicon an attractive platform for quantum computing. In recent years, hole spin qubits are being developed as they have the advantages of weak coupling to nuclear spin noise and strong spin-orbit coupling (SOC), in constructing high-fidelity quantum gates. However, there are relatively few studies on the hole spin qubits in a single acceptor, which requires only low density of the metallic gates. In particular, the investigation of flexible tunability using controllable strain for fault-tolerant quantum gates of acceptor-based qubits is still lacking. Here, we study the tunability of electric dipole spin resonance (EDSR) of acceptor-based hole spin qubits with controllable strain. The flexible tunability of LH-HH splitting and spin-hole coupling (SHC) with the two kinds of strain can avoid high electric field at the "sweet spot", and the operation performance of the acceptor qubits could be optimized. Longer relaxation time or stronger EDSR coupling at low electric field can be obtained. Moreover, with asymmetric strain, two "sweet spots" are induced and may merge together, and form a second-order "sweet spot". As a result, the quality factor $Q$ can reach $10^{4}$ for single-qubit operation, with high tolerance for the electric field variation. Furthermore, the two-qubit operation of acceptor qubits based on dipole-dipole interaction is discussed for high-fidelity two-qubit gates. The tunability of spin qubit properties in acceptor via strain could provide promising routes for spin-based quantum computing.

Flopping-mode spin qubit in a Si-MOS quantum dot

Spin qubits based on silicon metal-oxide semiconductor (Si-MOS) quantum dots (QDs) are promising platforms for large-scale quantum computers. To control spin qubits in QDs, electric dipole spin resonance (EDSR) has been most commonly used in recent years. By delocalizing an electron across a double quantum dots charge state, “flopping-mode” EDSR has been realized in Si/SiGe QDs. Here, we demonstrate a flopping-mode spin qubit in a Si-MOS QD via Elzerman single-shot readout. When changing the detuning with a fixed drive power, we achieve s-shape spin resonance frequencies, an order of magnitude improvement in the spin Rabi frequencies, and virtually constant spin dephasing times. Our results offer a route to large-scale spin qubit systems with higher control fidelity in Si-MOS QDs.

Combining n-MOS Charge Sensing with p-MOS Silicon Hole Double Quantum Dots in a CMOS platform.

Holes in silicon quantum dots are receiving attention due to their potential as fast, tunable, and scalable qubits in semiconductor quantum circuits. Despite this, challenges remain in this material system including difficulties using charge sensing to determine the number of holes in a quantum dot, and in controlling the coupling between adjacent quantum dots. We address these problems by fabricating an ambipolar complementary metal-oxide-semiconductor (CMOS) device using multilayer palladium gates. The device consists of an electron charge sensor adjacent to a hole double quantum dot. We demonstrate control of the spin state via electric dipole spin resonance. We achieve smooth control of the interdot coupling rate over 1 order of magnitude and use the charge sensor to perform spin-to-charge conversion to measure the hole singlet-triplet relaxation time of 11 μs for a known hole occupation. These results provide a path toward improving the quality and controllability of hole spin-qubits.

Spin dynamics in quantum dots on liquid helium

Liquid He-4 is free from magnetic defects, making it an ideal substrate for electrons with long-lived spin states. When electrons are localized in quantum dots and a strong magnetic field is applied along the surface, such states may serve as qubit states. A nonuniform magnetic field from a current-carrying wire submerged into helium enables switchable spin-orbit coupling. Bringing the frequency of orbital intradot vibrations close to the Larmor frequency allows for obtaining a strong Rashba electric dipole spin resonance and efficient interdot spin coupling. The authors show that the associated spin relaxation can be made sufficiently slow, permitting high-fidelity gate operations.

Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration

Electrons in Si/SiGe quantum dots are a promising platform for quantum computation. Many leading designs, however, rely on synthetic spin-orbit coupling arising from micromagnets, leading to challenges in scaling. Here, it is shown that the intrinsic spin-orbit coupling of the conduction-band valleys can be enhanced by over an order of magnitude by including Ge concentration oscillations of an appropriate wavelength within the quantum-well region. This enables fast spin manipulation using electric dipole spin resonance in the absence of micromagnets.

Electric-dipole spin resonance and spin orbit coupling effects in odd-integer quantum Hall edge channels

Structural-inversion-asymmetry effects on charge carriers can be described by a spin-orbit (Rashba) effective magnetic field. The direction of this field is fixed by the carrier momentum and axis of asymmetry - properties that form the basis of the spin transistor. The authors have used a sensitive terahertz magnetophotoresponse method to probe electrons in an asymmetric quantum well of InAs in the integer quantum-Hall-effect regime. Remarkable multiple-line spin-resonance spectra are attributed to oppositely directed Rashba fields of electrons in counterpropagating quasi-one-dimensional channels on opposite sample edges. Similar effects might lead to ultrafast electric-field control of spins for any spin-polarized topological edge channels.

Efficient spin generation in graphene by magnetic proximity effect upon absorption of far-IR radiation

The magnetic proximity effect is significant for atomically thin layers of two-dimensional materials. In this paper, we study the mechanisms of photogeneration spin-polarized carriers in graphene on a magnetic insulator. The magnetic proximity effect and lowered symmetry at the interface enhance the spin response of graphene in the alternating electric field of the incident light. The first leads to spin splitting of the linear spectrum of Dirac electrons. The second increases the role of the spin-orbit interaction. The main mechanisms of photogenerated spin polarization have been considered, including spin flip intersubband and interband transitions, and their contribution to the absorption coefficient of graphene. Keywords: Dirac electrons, graphene, electric dipole spin resonance, spin-orbit coupling, spin generation.

Micromagnet design for addressable fast spin manipulations in a 2 × 2 quantum dot array

The scaling up of semiconductor quantum dots to two-dimensional arrays is attracting considerable interest for use in large-scale spin-based quantum computation. One of the fundamental technologies to be realized in the two-dimensional arrays of quantum dots is the coherent manipulations of individual electron spins. In this work, we report on a micromagnet design that generates stray magnetic fields that can be used for spin manipulations via electric dipole spin resonance in a 2 × 2 quantum dot array. We consider a micromagnet with lower symmetry than that typically used in the case of linear dot arrays and optimize its dimensions to produce a maximum stray field gradient while maintaining Zeeman splitting differences sufficiently large among the four dots to permit qubit addressability. The optimized field gradient is around 60% smaller than that used in linear dot arrays, but it is still large enough for spin manipulation experiments. Our result represents an important step toward the experimental realization of spin-qubit operations in two-dimensional arrays of quantum dots.

Single-spin Landau-Zener-Stückelberg-Majorana interferometry of Zeeman-split states with strong spin-orbit interaction in a double quantum dot

Single spin state evolution induced by the Landau-Zener-St\"uckelberg-Majorana (LZSM) interference in a Zeeman-spit four level system in a periodically driven double quantum dot is studied theoretically by the Floquet stroboscopic method. An interplay between spin-conserving and spin-flip tunneling processes with the Electric Dipole Spin Resonance (EDSR) that is induced in an individual dot and enhanced by the LZSM multiple level crossings with the neighboring quantum dot is investigated as a function of the microwave (MW) frequency, driving amplitude, interdot detuning, and magnetic field. A number of special points in the parameter space are identified, out of which where all the three features are merged. Under this triple-crossing resonance condition the interdot tunneling is combined with a fast spin evolution in each dot at the EDSR frequency. Harmonics of the EDSR are revealed in the spin-dependent tunneling maps versus variable magnetic field and MW frequency. The results are applicable for both electron and hole systems with strong spin-orbit interaction and may be useful for developing new time-efficient schemes of the spin control and readout in qubit devices.

To 95-th birthday of Professor E.I. Rashba (looking back ones again)

The theory of spin-orbit interaction, developed by E.I. Rashba more than 30 years ago, stimulated the rapid development of a new discipline – spintronics – the physics of processes and devices based on the control of spins. The paper summarizes achievements of Prof. Rashba in the early stage of his scientific researches, particularly those, which were performed in Ukraine. Among them, prediction of electric dipole spin resonance (EDSR), phase transitions in spin-orbit coupled systems driven by change of the Fermi surface topology, giant oscillator strength of impurity excitons, and coexistence of free and self-trapped excitons. Solid state physics is the basis of contemporary electronics and optoelectronics. Various electronic, optical, acoustical and other effects and processes in solid define performances of modern solid state devices. Multitude of groups and thousands researchers are involved in discovering, study and using relevant new phenomena. Among them, Professor Emmanuel Rashba with his outstanding results in physics of crystals is seen (rises) as a profound personality. His contribution in almost all branches of solid state physics cannot be exaggerated, some of his results have found important applications. Prof. E.I. Rashba is known as one of the leading theorists in Ukraine, in Soviet Union, and he continued the successful career in United States. Although many years have already passed, scientific community in Ukraine remembers Prof. E.I. Rashba and thankfully appreciates his impact to formation of condensed matter researches in our country. This short text is devoted to Prof. E.I. Rashba and is written on the occasion of his birthday.

Zoo of silicon-based quantum bits

Zoo of silicon-based quantum bits

Electrical manipulation of a hole ‘spin’–orbit qubit in nanowire quantum dot: The nontrivial magnetic field effects

Strong ‘spin’–orbit coupled one-dimensional hole gas is achievable in a Ge nanowire in the presence of a strong magnetic field. The strong magnetic field lifts the two-fold degeneracy in the hole subband dispersions, so that the effective low-energy subband dispersion exhibits strong spin–orbit coupling. Here, we study the electrical spin manipulation in a Ge nanowire quantum dot for both the lowest and second lowest hole subband dispersions. Using a finite square well to model the quantum dot confining potential, we calculate exactly the level splitting of the spin–orbit qubit and the Rabi frequency in the electric-dipole spin resonance. The spin–orbit coupling modulated longitudinal g-factor g so is not only non-vanishing but also magnetic field dependent. Moreover, the spin–orbit couplings of the lowest and second lowest subband dispersions have opposite magnetic dependences, so that the results for these two subband dispersions are totally different. It should be noticed that we focus only on the properties of the hole ‘spin’ instead of the real hole spin.