1,767 research outputs found
Superradiance-like Electron Transport through a Quantum Dot
We theoretically show that intriguing features of coherent many-body physics
can be observed in electron transport through a quantum dot (QD). We first
derive a master equation based framework for electron transport in the
Coulomb-blockade regime which includes hyperfine (HF) interaction with the
nuclear spin ensemble in the QD. This general tool is then used to study the
leakage current through a single QD in a transport setting. We find that, for
an initially polarized nuclear system, the proposed setup leads to a strong
current peak, in close analogy with superradiant emission of photons from
atomic ensembles. This effect could be observed with realistic experimental
parameters and would provide clear evidence of coherent HF dynamics of nuclear
spin ensembles in QDs.Comment: 21 pages, 10 figure
Quantum correlations of light due to a room temperature mechanical oscillator for force metrology
The coupling of laser light to a mechanical oscillator via radiation pressure
leads to the emergence of quantum mechanical correlations between the amplitude
and phase quadrature of the laser beam. These correlations form a generic
non-classical resource which can be employed for quantum-enhanced force
metrology, and give rise to ponderomotive squeezing in the limit of strong
correlations. To date, this resource has only been observed in a handful of
cryogenic cavity optomechanical experiments. Here, we demonstrate the ability
to efficiently resolve optomechanical quantum correlations imprinted on an
optical laser field interacting with a room temperature nanomechanical
oscillator. Direct measurement of the optical field in a detuned homodyne
detector ("variational measurement") at frequencies far from the resonance
frequency of the oscillator reveal quantum correlations at the few percent
level. We demonstrate how the absolute visibility of these correlations can be
used for a quantum-enhanced estimation of the quantum back-action force acting
on the oscillator, and provides for an enhancement in the relative
signal-to-noise ratio for the estimation of an off-resonant external force,
even at room temperature
Hybrid Architecture for Engineering Magnonic Quantum Networks
We show theoretically that a network of superconducting loops and magnetic
particles can be used to implement magnonic crystals with tunable magnonic band
structures. In our approach, the loops mediate interactions between the
particles and allow magnetic excitations to tunnel over long distances. As a
result, different arrangements of loops and particles allow one to engineer the
band structure for the magnonic excitations. Furthermore, we show how magnons
in such crystals can serve as a quantum bus for long-distance magnetic coupling
of spin qubits. The qubits are coupled to the magnets in the network by their
local magnetic-dipole interaction and provide an integrated way to measure the
state of the magnonic quantum network.Comment: Manuscript: 4 pages, 3 figures. Supplemental Material: 9 pages, 4
figures. V2: Published version in PRA: 14 pages + 8 figures. Substantial
rearrangement of the content of the previous versio
Nuclear Spin Dynamics in Double Quantum Dots: Multi-Stability, Dynamical Polarization, Criticality and Entanglement
We theoretically study the nuclear spin dynamics driven by electron transport
and hyperfine interaction in an electrically-defined double quantum dot (DQD)
in the Pauli-blockade regime. We derive a master-equation-based framework and
show that the coupled electron-nuclear system displays an instability towards
the buildup of large nuclear spin polarization gradients in the two quantum
dots. In the presence of such inhomogeneous magnetic fields, a quantum
interference effect in the collective hyperfine coupling results in sizable
nuclear spin entanglement between the two quantum dots in the steady state of
the evolution. We investigate this effect using analytical and numerical
techniques, and demonstrate its robustness under various types of
imperfections.Comment: 35 pages, 19 figures. This article provides the full analysis of a
scheme proposed in Phys. Rev. Lett. 111, 246802 (2013). v2: version as
publishe
Solid-state magnetic traps and lattices
We propose and analyze magnetic traps and lattices for electrons in
semiconductors. We provide a general theoretical framework and show that
thermally stable traps can be generated by magnetically driving the particle's
internal spin transition, akin to optical dipole traps for ultra-cold atoms.
Next we discuss in detail periodic arrays of magnetic traps, i.e. magnetic
lattices, as a platform for quantum simulation of exotic Hubbard models, with
lattice parameters that can be tuned in real time. Our scheme can be readily
implemented in state-of-the-art experiments, as we particularize for two
specific setups, one based on a superconducting circuit and another one based
on surface acoustic waves.Comment: 18 pages, 8 figure
Expansion velocity of a one-dimensional, two-component Fermi gas during the sudden expansion in the ballistic regime
We show that in the sudden expansion of a spin-balanced two-component Fermi
gas into an empty optical lattice induced by releasing particles from a trap,
over a wide parameter regime, the radius of the particle cloud grows
linearly in time. This allow us to define the expansion velocity from
. The goal of this work is to clarify the dependence of the
expansion velocity on the initial conditions which we establish from
time-dependent density matrix renormalization group simulations, both for a box
trap and a harmonic trap. As a prominent result, the presence of a
Mott-insulating region leaves clear fingerprints in the expansion velocity. Our
predictions can be verified in experiments with ultra-cold atoms.Comment: 8 pages 10 figures, version as published with minor stylistic change
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