97 research outputs found
Quantum Simulation of Spin Chains Coupled to Bosonic Modes with Superconducting Circuits
We propose the implementation of a digital quantum simulation of spin chains
coupled to bosonic field modes in superconducting circuits. Gates with high
fidelities allows one to simulate a variety of Ising magnetic pairing
interactions with transverse field, Tavis-Cummings interaction between spins
and a bosonic mode, and a spin model with three-body terms. We analyze the
feasibility of the implementation in realistic circuit quantum electrodynamics
setups, where the interactions are either realized via capacitive couplings or
mediated by microwave resonators.Comment: Chapter in R. S. Anderssen et al. (eds.), Mathematics for Industry 11
(Springer Japan, 2015
Observation of coherent many-body Rabi oscillations
A two-level quantum system coherently driven by a resonant electromagnetic
field oscillates sinusoidally between the two levels at frequency
which is proportional to the field amplitude [1]. This phenomenon, known as the
Rabi oscillation, has been at the heart of atomic, molecular and optical
physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi
oscillations in isolated single atoms or dilute gases form the basis for
metrological applications such as atomic clocks and precision measurements of
physical constants [3]. Both inhomogeneous distribution of coupling strength to
the field and interactions between individual atoms reduce the visibility of
the oscillation and may even suppress it completely. A remarkable
transformation takes place in the limit where only a single excitation can be
present in the sample due to either initial conditions or atomic interactions:
there arises a collective, many-body Rabi oscillation at a frequency
involving all N >> 1 atoms in the sample [4]. This is true even
for inhomogeneous atom-field coupling distributions, where single-atom Rabi
oscillations may be invisible. When one of the two levels is a strongly
interacting Rydberg level, many-body Rabi oscillations emerge as a consequence
of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to
quantum information processing based on this effect [5]. Here we report initial
observations of coherent many-body Rabi oscillations between the ground level
and a Rydberg level using several hundred cold rubidium atoms. The strongly
pronounced oscillations indicate a nearly complete excitation blockade of the
entire mesoscopic ensemble by a single excited atom. The results pave the way
towards quantum computation and simulation using ensembles of atoms
Electrical detection of 31P spin quantum states
In recent years, a variety of solid-state qubits has been realized, including
quantum dots, superconducting tunnel junctions and point defects. Due to its
potential compatibility with existing microelectronics, the proposal by Kane
based on phosphorus donors in Si has also been pursued intensively. A key issue
of this concept is the readout of the P quantum state. While electrical
measurements of magnetic resonance have been performed on single spins, the
statistical nature of these experiments based on random telegraph noise
measurements has impeded the readout of single spin states. In this letter, we
demonstrate the measurement of the spin state of P donor electrons in silicon
and the observation of Rabi flops by purely electric means, accomplished by
coherent manipulation of spin-dependent charge carrier recombination between
the P donor and paramagnetic localized states at the Si/SiO2 interface via
pulsed electrically detected magnetic resonance. The electron spin information
is shown to be coupled through the hyperfine interaction with the P nucleus,
which demonstrates the feasibility of a recombination-based readout of nuclear
spins
Ballistic Spin Resonance
The phenomenon of spin resonance has had far reaching influence since its
discovery nearly 70 years ago. Electron spin resonance (ESR) driven by high
frequency magnetic fields has informed our understanding of quantum mechanics,
and finds application in fields as diverse as medicine and quantum information.
Spin resonance induced by high frequency electric fields, known as electric
dipole spin resonance (EDSR), has also been demonstrated recently. EDSR is
mediated by spin-orbit interaction (SOI), which couples the spin degree of
freedom and the momentum vector. Here, we report the observation of a novel
spin resonance due to SOI that does not require external driving fields.
Ballistic spin resonance (BSR) is driven by an internal spin-orbit field that
acts upon electrons bouncing at gigaHertz frequencies in narrow channels of
ultra-clean two-dimensional electron gas (2DEG). BSR is manifested in
electrical measurements of pure spin currents as a strong suppression of spin
relaxation length when the motion of electrons is in resonance with spin
precession. These findings point the way to gate-tunable coherent spin
rotations in ballistic nanostructures without external a.c. fields.Comment: 24 pages, including supplementary material
Qubit-flip-induced cavity mode squeezing in the strong dispersive regime of the quantum Rabi model
Squeezed states of light are a set of nonclassical states in which the quantum fluctuations of one quadrature component are reduced below the standard quantum limit. With less noise than the best stabilised laser sources, squeezed light is a key resource in the field of quantum technologies and has already improved sensing capabilities in areas ranging from gravitational wave detection to biomedical applications. In this work we propose a novel technique for generating squeezed states of a confined light field strongly coupled to a two-level system, or qubit, in the dispersive regime. Utilising the dispersive energy shift caused by the interaction, control of the qubit state produces a time-dependent change in the frequency of the light field. An appropriately timed sequence of sudden frequency changes reduces the quantum noise fluctuations in one quadrature of the field well below the standard quantum limit. The degree of squeezing and the time of generation are directly controlled by the number of frequency shifts applied. Even in the presence of realistic noise and imperfections, our protocol promises to be capable of generating a useful degree of squeezing with present experimental capabilities
Nanoscale magnetic imaging of a single electron spin under ambient conditions
The detection of ensembles of spins under ambient conditions has revolutionized the biological, chemical and physical sciences through magnetic resonance imaging and nuclear magnetic resonance . Pushing sensing capabilities to the individual-spin level would enable unprecedented applications such as single-molecule structural imaging; however, the weak magnetic fields from single spins are undetectable by conventional far-field resonance techniques . In recent years, there has been a considerable effort to develop nanoscale scanning magnetometers , which are able to measure fewer spins by bringing the sensor in close proximity to its target. The most sensitive of these magnetometers generally require low temperatures for operation, but the ability to measure under ambient conditions (standard temperature and pressure) is critical for many imaging applications, particularly in biological systems. Here we demonstrate detection and nanoscale imaging of the magnetic field from an initialized single electron spin under ambient conditions using a scanning nitrogen-vacancy magnetometer. Real-space, quantitative magnetic-field images are obtained by deterministically scanning our nitrogen-vacancy magnetometer 50 nm above a target electron spin, while measuring the local magnetic field using dynamically decoupled magnetometry protocols. We discuss how this single-spin detection enables the study of a variety of room-temperature phenomena in condensed-matter physics with an unprecedented combination of spatial resolution and spin sensitivity
Rare-earth solid-state qubits
Quantum bits (qubits) are the basic building blocks of any quantum computer.
Superconducting qubits have been created with a 'top-down' approach that
integrates superconducting devices into macroscopic electrical circuits [1-3],
whereas electron-spin qubits have been demonstrated in quantum dots [4-6]. The
phase coherence time (Tau2) and the single qubit figure of merit (QM) of
superconducting and electron-spin qubits are similar -- Tau2 ~ microseconds and
QM ~10-1000 below 100mK -- and it should be possible to scale-up these systems,
which is essential for the development of any useful quantum computer.
Bottom-up approaches based on dilute ensembles of spins have achieved much
larger values of tau2 (up to tens of ms) [7, 8], but these systems cannot be
scaled up, although some proposals for qubits based on 2D nanostructures should
be scalable [9-11]. Here we report that a new family of spin qubits based on
rare-earth ions demonstrates values of Tau2 (~ 50microseconds) and QM (~1400)
at 2.5 K, which suggests that rare-earth qubits may, in principle, be suitable
for scalable quantum information processing at 4He temperatures
Quantum dynamics in strong fluctuating fields
A large number of multifaceted quantum transport processes in molecular
systems and physical nanosystems can be treated in terms of quantum relaxation
processes which couple to one or several fluctuating environments. A thermal
equilibrium environment can conveniently be modelled by a thermal bath of
harmonic oscillators. An archetype situation provides a two-state dissipative
quantum dynamics, commonly known under the label of a spin-boson dynamics. An
interesting and nontrivial physical situation emerges, however, when the
quantum dynamics evolves far away from thermal equilibrium. This occurs, for
example, when a charge transferring medium possesses nonequilibrium degrees of
freedom, or when a strong time-dependent control field is applied externally.
Accordingly, certain parameters of underlying quantum subsystem acquire
stochastic character. Herein, we review the general theoretical framework which
is based on the method of projector operators, yielding the quantum master
equations for systems that are exposed to strong external fields. This allows
one to investigate on a common basis the influence of nonequilibrium
fluctuations and periodic electrical fields on quantum transport processes.
Most importantly, such strong fluctuating fields induce a whole variety of
nonlinear and nonequilibrium phenomena. A characteristic feature of such
dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres
The deuteron: structure and form factors
A brief review of the history of the discovery of the deuteron in provided.
The current status of both experiment and theory for the elastic electron
scattering is then presented.Comment: 80 pages, 33 figures, submited to Advances in Nuclear Physic
Noninertial effects on a Dirac neutral particle inducing an analogue of the Landau quantization in the cosmic string spacetime
We discuss the behaviour of external fields that interact with a Dirac
neutral particle with a permanent electric dipole moment in order to achieve
relativistic bound states solutions in a noninertial frame and in the presence
of a topological defect spacetime. We show that the noninertial effects of the
Fermi-Walker reference frame induce a radial magnetic field even in the absence
of magnetic charges, which is influenced by the topology of the cosmic string
spacetime. We then discuss the conditions that the induced fields must satisfy
to yield the relativistic bound states corresponding to the
Landau-He-McKellar-Wilkens quantization in the cosmic string spacetime. Finally
we obtain the Dirac spinors for positive-energy solutions and the Gordon
decomposition of the Dirac probability current.Comment: 15 pages, no figure, this paper will be published in volume 42 of the
Brazilian Journal of Physic
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