5,325 research outputs found
Interacting atomic interferometry for rotation sensing approaching the Heisenberg Limit
Atom interferometers provide exquisite measurements of the properties of
non-inertial frames. While atomic interactions are typically detrimental to
good sensing, efforts to harness entanglement to improve sensitivity remain
tantalizing. Here we explore the role of interactions in an analogy between
atomic gyroscopes and SQUIDs, motivated by recent experiments realizing ring
shaped traps for ultracold atoms. We explore the one-dimensional limit of these
ring systems with a moving weak barrier, such as that provided by a
blue-detuned laser beam. In this limit, we employ Luttinger liquid theory and
find an analogy with the superconducting phase-slip qubit, in which the
topological charge associated with persistent currents can be put into
superposition. In particular, we find that strongly-interacting atoms in such a
system could be used for precision rotation sensing. We compare the performance
of this new sensor to an equivalent non-interacting atom interferometer, and
find improvements in sensitivity and bandwidth beyond the atomic shot-noise
limit.Comment: 18 pages, 4 figure
Algorithmic Cooling of a Quantum Simulator
Controlled quantum mechanical devices provide a means of simulating more
complex quantum systems exponentially faster than classical computers. Such
"quantum simulators" rely heavily upon being able to prepare the ground state
of Hamiltonians, whose properties can be used to calculate correlation
functions or even the solution to certain classical computations. While
adiabatic preparation remains the primary means of producing such ground
states, here we provide a different avenue of preparation: cooling to the
ground state via simulated dissipation. This is in direct analogy to
contemporary efforts to realize generalized forms of simulated annealing in
quantum systems.Comment: 41 pages, 2 figue
Blind quantum computation using the central spin Hamiltonian
Blindness is a desirable feature in delegated computation. In the classical
setting, blind computations protect the data or even the program run by a
server. In the quantum regime, blind computing may also enable testing
computational or other quantum properties of the server system. Here we propose
a scheme for universal blind quantum computation using a quantum simulator
capable of emulating Heisenberg-like Hamiltonians. Our scheme is inspired by
the central spin Hamiltonian in which a single spin controls dynamics of a
number of bath spins. We show how, by manipulating this spin, a client that
only accesses the central spin can effectively perform blind computation on the
bath spins. Remarkably, two-way quantum communication mediated by the central
spin is sufficient to ensure security in the scheme. Finally, we provide
explicit examples of how our universal blind quantum computation enables
verification of the power of the server from classical to stabilizer to full
BQP computation.Comment: 8 pages, 2 figure
A Quantum Model for Entropic Springs
Motivated by understanding the emergence of thermodynamic restoring forces
and oscillations, we develop a quantum-mechanical model of a bath of spins
coupled to the elasticity of a material. We show our model reproduces the
behavior of a variety of entropic springs while enabling investigation of
non-equilibrium resonator states in the quantum domain. We find our model
emerges naturally in disordered elastic media such as glasses, and is an
additional, expected effect in systems with anomalous specific heat and 1/f
noise at low temperatures due to two-level systems that fluctuate.Comment: 7 pages, 4 figure
Optomechanical approach to controlling the temperature and chemical potential of light
Massless particles, including photons, are not governed by particle
conservation law during their typical interaction with matter even at low
energies, and thus have no chemical potential. However, in driven systems, near
equilibrium dynamics can lead to equilibration of photons with a finite number,
describable using an effective chemical potential [M. Hafezi et al., Phys. Rev.
B 92, 174305 (2015)]. Here we build upon this general concept with an
implementation appropriate for a photon-based quantum simulator. We consider
how laser cooling of a well-isolated mechanical mode can provide an effective
low-frequency bath for the quantum simulator system. We show that the use of
auxiliary photon modes, coupled by the mechanical system, enables control of
both the chemical potential and temperature of the resulting photonic quantum
simulator's grand canonical ensemble.Comment: 10 pages, 4 figure
Quantum Nonlinear Optics Near Optomechanical Instabilities
Optomechanical systems provide a unique platform for observing quantum
behavior of macroscopic objects. However, efforts towards realizing nonlinear
behavior at the single photon level have been inhibited by the small size of
the radiation pressure interaction. Here we show that it is not necessary to
reach the single-photon strong-coupling regime in order to realize significant
optomechanical nonlinearities. Instead, nonlinearities at the few quanta level
can be achieved, even with weak-coupling, in a two-mode optomechanical system
driven near instability. In this limit, we establish a new figure of merit for
realizing strong nonlinearity which scales with the single-photon
optomechanical coupling and the sideband resolution of the mechanical mode with
respect to the cavity linewidth. We find that current devices based on
optomechanical crystals, thought to be in the weak-coupling regime, can still
achieve strong quantum nonlinearity; enabling deterministic interactions
between single photons.Comment: 6+3 pages, 3 figure
Engineering three-body interaction and Pfaffian states in circuit QED systems
We demonstrate a scheme to engineer the three-body interaction in circuit-QED
systems by tuning a fluxonium qubit. Connecting such qubits in a square lattice
and controlling the tunneling dynamics, in the form of a synthesized magnetic
field, for the photon-like excitations of the system, allows the implementation
of a parent Hamiltonian whose ground state is the Pfaffian wave function.
Furthermore, we show that the addition of the next-nearest neighbor tunneling
stabilizes the ground state, recovering the expected topological degeneracy
even for small lattices. Finally, we discuss the implementation of these ideas
with the current technology.Comment: 5 pages, 4 figure
Interferometry with Synthetic Gauge Fields
We propose a compact atom interferometry scheme for measuring weak,
time-dependent accelerations. Our proposal uses an ensemble of dilute trapped
bosons with two internal states that couple to a synthetic gauge field with
opposite charges. The trapped gauge field couples spin to momentum to allow
time dependent accelerations to be continuously imparted on the internal
states. We generalize this system to reduce noise and estimate the sensitivity
of such a system to be S~10^-7 m / s^2 / Hz^1/2
Dynamic suppression of Rayleigh light scattering in dielectric resonators
The ultimate limits of performance for any classical optical system are set
by sub-wavelength fluctuations within the host material, that may be frozen-in
or even dynamically induced. The most common manifestation of such
sub-wavelength disorder is Rayleigh light scattering, which is observed in
nearly all wave-guiding technologies today and can lead to both irreversible
radiative losses as well as undesirable intermodal coupling. While it has been
shown that backscattering from disorder can be suppressed by breaking
time-reversal symmetry in magneto-optic and topological insulator materials,
common optical dielectrics possess neither of these properties. Here we
demonstrate an optomechanical approach for dynamically suppressing Rayleigh
backscattering within dielectric resonators. We achieve this by locally
breaking time-reversal symmetry in a silica resonator through a Brillouin
scattering interaction that is available in all materials. Near-complete
suppression of Rayleigh backscattering is experimentally confirmed through
three independent measurements -- the reduction of the back-reflections caused
by scatterers, the elimination of a commonly seen normal-mode splitting effect,
and by measurement of the reduction in intrinsic optical loss. More broadly,
our results provide new evidence that it is possible to dynamically suppress
Rayleigh backscattering within any optical dielectric medium, for achieving
robust light propagation in nanophotonic devices in spite of the presence of
scatterers or defects.Comment: 14 pages, 3 figures with supplementary informatio
Dynamics of an Ion Coupled to a Parametric Superconducting Circuit
Superconducting circuits and trapped ions are promising architectures for
quantum information processing. However, the natural frequencies for
controlling these systems -- radio frequency ion control and microwave domain
superconducting qubit control -- make direct Hamiltonian interactions between
them weak. In this paper we describe a technique for coupling a trapped ion's
motion to the fundamental mode of a superconducting circuit, by applying to the
circuit a carefully modulated external magnetic flux. In conjunction with a
non-linear element (Josephson junction), this gives the circuit an effective
time-dependent inductance. We then show how to tune the external flux to
generate a resonant coupling between the circuit and ion's motional mode, and
discuss the limitations of this approach compared to using a time-dependent
capacitance.Comment: 10 pages, 4 figure
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