201 research outputs found
Optomechanics assisted with a qubit: From dissipative state preparation to many-body physics
We propose and analyze nonlinear optomechanical protocols that can be
implemented by adding a single atom to an optomechanical cavity. In particular,
we show how to engineer the environment in order to dissipatively prepare the
mechanical oscillator in a superposition of Fock states with fidelity close to
one. Furthermore, we discuss how a single atom in a cavity with several
mechanical oscillators can be exploited to realize nonlinear many-body physics
by stroboscopically driving the mechanical oscillators. We show how to prepare
non-classical many-body states by either applying coherent protocols or
engineering dissipation. The analysis of the protocols is carried out using a
perturbation theory for degenerate Liouvillians and numerical tools. Our
results apply to other systems where a qubit is coupled to a mechanical
oscillator via a bosonic mode, e.g., in cavity quantum electromechanics
Quantum Ratchets for Quantum Communication with Optical Superlattices
We propose to use a quantum ratchet to transport quantum information in a
chain of atoms trapped in an optical superlattice. The quantum ratchet is
created by a continuous modulation of the optical superlattice which is
periodic in time and in space. Though there is zero average force acting on the
atoms, we show that indeed the ratchet effect permits atoms on even and odd
sites to move along opposite directions. By loading the optical lattice with
two-level bosonic atoms, this scheme permits to perfectly transport a qubit or
entangled state imprinted in one or more atoms to any desired position in the
lattice. From the quantum computation point of view, the transport is achieved
by a smooth concatenation of perfect swap gates. We analyze setups with
noninteracting and interacting particles and in the latter case we use the
tools of optimal control to design optimal modulations. We also discuss the
feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure
Master equation approach to optomechanics with arbitrary dielectrics
We present a master equation describing the interaction of light with
dielectric objects of arbitrary sizes and shapes. The quantum motion of the
object, the quantum nature of light, as well as scattering processes to all
orders in perturbation theory are taken into account. This formalism extends
the standard master equation approach to the case where interactions among
different modes of the environment are considered. It yields a genuine quantum
description, including a renormalization of the couplings and decoherence
terms. We apply this approach to analyze cavity cooling of the center-of-mass
mode of large spheres. Furthermore, we derive an expression for the
steady-state phonon numbers without relying on resolved-sideband or bad-cavity
approximations.Comment: 17 pages, 5 figure
Linear Stability Analysis of a Levitated Nanomagnet in a Static Magnetic Field: Quantum Spin Stabilized Magnetic Levitation
We theoretically study the levitation of a single magnetic domain nanosphere
in an external static magnetic field. We show that apart from the stability
provided by the mechanical rotation of the nanomagnet (as in the classical
Levitron), the quantum spin origin of its magnetization provides two additional
mechanisms to stably levitate the system. Despite of the Earnshaw theorem, such
stable phases are present even in the absence of mechanical rotation. For large
magnetic fields, the Larmor precession of the quantum magnetic moment
stabilizes the system in full analogy with magnetic trapping of a neutral atom.
For low magnetic fields, the magnetic anisotropy stabilizes the system via the
Einstein-de Haas effect. These results are obtained with a linear stability
analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy
in a Ioffe-Pritchard magnetic field.Comment: Published version. 10 pages, 4 figures, 3 table
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
Quantum Spin Stabilized Magnetic Levitation
We theoretically show that, despite Earnshaw's theorem, a non-rotating single
magnetic domain nanoparticle can be stably levitated in an external static
magnetic field. The stabilization relies on the quantum spin origin of
magnetization, namely the gyromagnetic effect. We predict the existence of two
stable phases related to the Einstein--de Haas effect and the Larmor
precession. At a stable point, we derive a quadratic Hamiltonian that describes
the quantum fluctuations of the degrees of freedom of the system. We show that
in the absence of thermal fluctuations, the quantum state of the nanomagnet at
the equilibrium point contains entanglement and squeezing.Comment: Published version. 5 pages, 2 figure
Superconducting Vortex Lattices for Ultracold Atoms
We propose and analyze a nanoengineered vortex array in a thin-film type-II
superconductor as a magnetic lattice for ultracold atoms. This proposal
addresses several of the key questions in the development of atomic quantum
simulators. By trapping atoms close to the surface, tools of nanofabrication
and structuring of lattices on the scale of few tens of nanometers become
available with a corresponding benefit in energy scales and temperature
requirements. This can be combined with the possibility of magnetic single site
addressing and manipulation together with a favorable scaling of
superconducting surface-induced decoherence.Comment: Published Version. Manuscript: 5 pages, 3 figures. Supplementary
Information: 11 pages, 7 figure
Transport and Entanglement Generation in the Bose-Hubbard Model
We study entanglement generation via particle transport across a
one-dimensional system described by the Bose-Hubbard Hamiltonian. We analyze
how the competition between interactions and tunneling affects transport
properties and the creation of entanglement in the occupation number basis.
Alternatively, we propose to use spatially delocalized quantum bits, where a
quantum bit is defined by the presence of a particle either in a site or in the
adjacent one. Our results can serve as a guidance for future experiments to
characterize entanglement of ultracold gases in one-dimensional optical
lattices.Comment: 14 pages, 6 figure
On optical forces in spherical whispering gallery mode resonators
In this paper we discuss the force exerted by the field of an optical cavity
on a polarizable dipole. We show that the modification of the cavity modes due
to interaction with the dipole significantly alters the properties of the
force. In particular, all components of the force are found to be
non-conservative, and cannot, therefore, be derived from a potential energy. We
also suggest a simple generalization of the standard formulas for the optical
force on the dipole, which reproduces the results of calculations based on the
Maxwell stress tensor.Comment: To pe published in Optics Express Focus Issue: "Collective phenomena
in photonic, plasmonic and hybrid structures
Large Quantum Superpositions and Interference of Massive Nanometer-Sized Objects
We propose a method to prepare and verify spatial quantum superpositions of a
nanometer-sized object separated by distances of the order of its size. This
method provides unprecedented bounds for objective collapse models of the wave
function by merging techniques and insights from cavity quantum optomechanics
and matter wave interferometry. An analysis and simulation of the experiment is
performed taking into account standard sources of decoherence. We provide an
operational parameter regime using present day and planned technology.Comment: 4 pages, 2 figures, to appear in PR
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