27 research outputs found
Sub-Poissonian Phonon Lasing in Three-Mode Optomechanics
We propose to use the resonant enhancement of the parametric instability in
an optomechanical system of two optical modes coupled to a mechanical
oscillator to prepare mechanical states with sub-Poissonian phonon statistics.
Strong single photon coupling is not required. The requirements regarding
sideband resolution, circulating cavity power and environmental temperature are
in reach with state of the art parameters of optomechanical crystals. Phonon
antibunching can be verfied in a Hanburry-Brown-Twiss measurement on the output
field of the optomechanical cavity.Comment: 6 pages, 4 figure
Unraveling nonclassicality in the optomechanical instability
Conditional dynamics due to continuous optical measurements has successfully
been applied for state reconstruction and feedback cooling in optomechanical
systems. In this article, we show that the same measurement techniques can be
used to unravel nonclassicality in optomechanical limit cycles. In contrast to
unconditional dynamics, our approach gives rise to nonclassical limit cycles
even in the sideband-unresolved regime, where the cavity decay rate exceeds the
mechanical frequency. We predict a significant reduction of the mechanical
amplitude fluctuations for realistic experimental parameters.Comment: 8 pages, 5 figures, equivalent to published versio
Long-lived qubit from three spin-1/2 atoms
A system of three spin-1/2 atoms allows the construction of a
reference-frame-free (RFF) qubit in the subspace with total angular momentum
. The RFF qubit stays coherent perfectly as long as the spins of the
three atoms are affected homogeneously. The inhomogeneous evolution of the
atoms causes decoherence, but this decoherence can be suppressed efficiently by
applying a bias magnetic field of modest strength perpendicular to the plane of
the atoms. The resulting lifetime of the RFF qubit can be many days, making RFF
qubits of this kind promising candidates for quantum information storage units.
Specifically, we examine the situation of three atoms trapped
in a -laser-generated optical lattice and find that, with
conservatively estimated parameters, a stored qubit maintains a fidelity of
0.9999 for two hours.Comment: 15 pages, 9 figures; version 2 reports a much improved analysis;
version 3 contains more details about the four-atom cas
Divergence of predictive model output as indication of phase transitions
We introduce a new method to identify phase boundaries in physical systems.
It is based on training a predictive model such as a neural network to infer a
physical system's parameters from its state. The deviation of the inferred
parameters from the underlying correct parameters will be most susceptible and
diverge maximally in the vicinity of phase boundaries. Therefore, peaks in the
divergence of the model's predictions are used as indication of phase
transitions. Our method is applicable for phase diagrams of arbitrary parameter
dimension and without prior information about the phases. Application to both
the two-dimensional Ising model and the dissipative Kuramoto-Hopf model show
promising results.Comment: 6 pages, 3 figure
Laser theory for quantum optomechanics
[no abstract
Quantum state preparation for coupled period tripling oscillators
We investigate the quantum transition to a correlated state of coupled
oscillators in the regime where they display period tripling in response to a
drive at triple the eigenfrequency. Correlations are formed between the
discrete oscillation phases of individual oscillators. The evolution toward the
ordered state is accompanied by the transient breaking of the symmetry between
seemingly equivalent configurations. We attribute this to the nontrivial
geometric phase that characterizes period tripling. We also show that the
Wigner distribution of a single damped quantum oscillator can display a minimum
at the classically stable zero-amplitude state.Comment: 7 pages, 9 figure
Fast Detection of Phase Transitions with Multi-Task Learning-by-Confusion
Machine learning has been successfully used to study phase transitions. One
of the most popular approaches to identifying critical points from data without
prior knowledge of the underlying phases is the learning-by-confusion scheme.
As input, it requires system samples drawn from a grid of the parameter whose
change is associated with potential phase transitions. Up to now, the scheme
required training a distinct binary classifier for each possible splitting of
the grid into two sides, resulting in a computational cost that scales linearly
with the number of grid points. In this work, we propose and showcase an
alternative implementation that only requires the training of a single
multi-class classifier. Ideally, such multi-task learning eliminates the
scaling with respect to the number of grid points. In applications to the Ising
model and an image dataset generated with Stable Diffusion, we find significant
speedups that closely correspond to the ideal case, with only minor deviations.Comment: 7 pages, 3 figures, Machine Learning and the Physical Sciences
Workshop, NeurIPS 202
Laser Theory for Optomechanics: Limit Cycles in the Quantum Regime
Optomechanical systems can exhibit self-sustained limit cycles where the
quantum state of the mechanical resonator possesses nonclassical
characteristics such as a strongly negative Wigner density, as was shown
recently in a numerical study by Qian et al. [Physical Review Letters, 109,
253601 (2012)]. Here we derive a Fokker-Planck equation describing mechanical
limit cycles in the quantum regime which correctly reproduces the numerically
observed nonclassical features. The derivation starts from the standard
optomechanical master equation, and is based on techniques borrowed from the
laser theory due to Haake's and Lewenstein. We compare our analytical model
with numerical solutions of the master equation based on Monte-Carlo
simulations, and find very good agreement over a wide and so far unexplored
regime of system parameters. As one main conclusion, we predict negative Wigner
functions to be observable even for surprisingly classical parameters, i.e.
outside the single-photon strong coupling regime, for strong cavity drive, and
rather large limit cycle amplitudes. The general approach taken here provides a
natural starting point for further studies of quantum effects in optomechanics.Comment: 17 pages, 7 figure
Unsupervised identification of topological order using predictive models
Machine-learning driven models have proven to be powerful tools for the
identification of phases of matter. In particular, unsupervised methods hold
the promise to help discover new phases of matter without the need for any
prior theoretical knowledge. While for phases characterized by a broken
symmetry, the use of unsupervised methods has proven to be successful,
topological phases without a local order parameter seem to be much harder to
identify without supervision. Here, we use an unsupervised approach to identify
topological phases and transitions out of them. We train artificial neural nets
to relate configurational data or measurement outcomes to quantities like
temperature or tuning parameters in the Hamiltonian. The accuracy of these
predictive models can then serve as an indicator for phase transitions. We
successfully illustrate this approach on both the classical Ising gauge theory
as well as on the quantum ground state of a generalized toric code.Comment: 12 pages, 13 figure
Quantum Algorithmic Readout in Multi-Ion Clocks
Optical clocks based on ensembles of trapped ions offer the perspective of
record frequency uncertainty with good short-term stability. Most suitable
atomic species lack closed transitions for fast detection such that the clock
signal has to be read out indirectly through transferring the quantum state of
clock ions to co-trapped logic ions by means of quantum logic operations. For
ensembles of clock ions existing methods for quantum logic readout require a
linear overhead in either time or the number of logic ions. Here we report a
quantum algorithmic readout whose overhead scales logarithmically with the
number of clock ions in both of these respects. We show that the readout
algorithm can be implemented with a single application of a multi-species
quantum gate, which we describe in detail for a crystal of Aluminum and Calcium
ions.Comment: 4 pages + 7 pages appendix; 5 figures; v3: published versio