20 research outputs found
Local Kondo temperatures in atomic chains
We study the effect of disorder in strongly interacting small atomic chains.
Using the Kotliar- Ruckenstein slave-boson approach we diagonalize the
Hamiltonian via scattering matrix theory. We numerically solve the Kondo
transmission and the slave-boson parameters that allow us to calculate the
Kondo temperature. We demonstrate that in the weak disorder regime, disorder in
the energy levels of the dopants induces a non-screened disorder in the Kondo
couplings of the atoms. We show that disorder increases the Kondo temperature
of a perfect chain. We find that this disorder in the couplings comes from a
local distribution of Kondo temperatures along the chain. We propose two
experimental setups where the impact of local Kondo temperatures can be
observed
Charge-Insensitive Single-Atom Spin-Orbit Qubit in Silicon
High fidelity entanglement of an on-chip array of spin qubits poses many
challenges. Spin-orbit coupling (SOC) can ease some of these challenges by
enabling long-ranged entanglement via electric dipole-dipole interactions,
microwave photons, or phonons. However, SOC exposes conventional spin qubits to
decoherence from electrical noise. Here we propose an acceptor-based spin-orbit
qubit in silicon offering long-range entanglement at a sweet spot where the
qubit is protected from electrical noise. The qubit relies on quadrupolar SOC
with the interface and gate potentials. As required for surface codes,
electrically mediated single-qubit and dipole-dipole mediated two-qubit
gates are possible in the predicted spin lifetime. Moreover, circuit quantum
electrodynamics with single spins is feasible, including dispersive readout,
cavity-mediated entanglement, and spin-photon entanglement. An industrially
relevant silicon-based platform is employed.Comment: 4 pages, 2 figure
Electrical operation of planar Ge hole spin qubits in an in-plane magnetic field
In this work we present a comprehensive theory of spin physics in planar Ge
hole quantum dots in an in-plane magnetic field, where the orbital terms play a
dominant role in qubit physics, and provide a brief comparison with
experimental measurements of the angular dependence of electrically driven spin
resonance. We focus the theoretical analysis on electrical spin operation,
phonon-induced relaxation, and the existence of coherence sweet spots. We find
that the choice of magnetic field orientation makes a substantial difference
for the properties of hole spin qubits. Furthermore, although the
Schrieffer-Wolff approximation can describe electron dipole spin resonance
(EDSR), it does not capture the fundamental spin dynamics underlying qubit
coherence. Specifically, we find that: (i) EDSR for in-plane magnetic fields
varies non-linearly with the field strength and weaker than for perpendicular
magnetic fields; (ii) The EDSR Rabi frequency is maximized when the a.c.
electric field is aligned parallel to the magnetic field, and vanishes when the
two are perpendicular; (iii) The Rabi ratio , i.e. the number of
EDSR gate operation per unit relaxation time, is expected to be as large as
at the magnetic fields used experimentally; (iv) The orbital
magnetic field terms make the in-plane -factor strongly anisotropic in a
squeezed dot, in excellent agreement with experimental measurements; (v) The
coherence sweet spots do not exist in an in-plane magnetic field, as the
orbital magnetic field terms expose the qubit to all components of the defect
electric field. These findings will provide a guideline for experiments to
design ultrafast, highly coherent hole spin qubits in Ge
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Roadmap on quantum nanotechnologies
Quantum phenomena are typically observable at length and time scales smaller than those of our everyday experience, often involving individual particles or excitations. The past few decades have seen a revolution in the ability to structure matter at the nanoscale, and experiments at the single particle level have become commonplace. This has opened wide new avenues for exploring and harnessing quantum mechanical effects in condensed matter. These quantum phenomena, in turn, have the potential to revolutionize the way we communicate, compute and probe the nanoscale world. Here, we review developments in key areas of quantum research in light of the nanotechnologies that enable them, with a view to what the future holds. Materials and devices with nanoscale features are used for quantum metrology and sensing, as building blocks for quantum computing, and as sources and detectors for quantum communication. They enable explorations of quantum behaviour and unconventional states in nano- and opto-mechanical systems, low-dimensional systems, molecular devices, nano-plasmonics, quantum electrodynamics, scanning tunnelling microscopy, and more. This rapidly expanding intersection of nanotechnology and quantum science/technology is mutually beneficial to both fields, laying claim to some of the most exciting scientific leaps of the last decade, with more on the horizon