25 research outputs found
Quantum-state steering in optomechanical devices
We show that optomechanical systems in the quantum regime can be used to
demonstrate EPR-type quantum entanglement between the optical field and the
mechanical oscillator, via quantum-state steering. Namely, the conditional
quantum state of the mechanical oscillator can be steered into different
quantum states depending the choice made on which quadrature of the out-going
field is to be measured via homodyne detection. More specifically, if quantum
radiation pressure force dominates over thermal force, the oscillator's quantum
state is steerable with a photodetection efficiency as low as 50%, approaching
the ideal limit shown by Wiseman and Gambetta [Phys. Rev. Lett. 108,
220402 (2012)]. We also show that requirement for steerability is the same as
those for achieving sub-Heisenberg state tomography using the same experimental
setup
Double optical spring enhancement for gravitational-wave detectors
Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance—which is upshifted from the pendulum frequency due to the so-called optical-spring effect. As an alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in reshaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization
Creation of a quantum oscillator by classical control
As a pure quantum state is being approached via linear feedback, and the
occupation number approaches and eventually goes below unity, optimal control
becomes crucial. We obtain theoretically the optimal feedback controller that
minimizes the uncertainty for a general linear measurement process, and show
that even in the absence of classical noise, a pure quantum state is not always
achievable via feedback. For Markovian measurements, the deviation from minimum
Heisenberg Uncertainty is found to be closely related to the extent to which
the device beats the free-mass Standard Quantum Limit for force measurement. We
then specialize to optical Markovian measurements, and demonstrate that a
slight modification to the usual input-output scheme -- either injecting
frequency independent squeezed vacuum or making a homodyne detection at a
non-phase quadrature -- allows controlled states of kilogram-scale mirrors in
future LIGO interferometers to reach occupation numbers significantly below
unity.Comment: 4 pages, 2 figure
Preparing a mechanical oscillator in non-Gaussian quantum states
We propose a protocol for coherently transferring non-Gaussian quantum states
from optical field to a mechanical oscillator. The open quantum dynamics and
continuous-measurement process, which can not be treated by the
stochastic-master-equation formalism, are studied by a new path-integral-based
approach. We obtain an elegant relation between the quantum state of the
mechanical oscillator and that of the optical field, which is valid for general
linear quantum dynamics. We demonstrate the experimental feasibility of such
protocol by considering the cases of both large-scale gravitational-wave
detectors and small-scale cavity-assisted optomechanical devices.Comment: 4 pages, 3 figure
Entanglement of macroscopic test masses and the Standard Quantum Limit in laser interferometry
We show that the generation of entanglement of two heavily macroscopic
mirrors with masses of up to several kilograms are feasible with state of the
art techniques of high-precision laser interferometry. The basis of such a
demonstration would be a Michelson interferometer with suspended mirrors and
simultaneous homodyne detections at both interferometer output ports. We
present the connection between the generation of entanglement and the Standard
Quantum Limit (SQL) for a free mass. The SQL is a well-known reference limit in
operating interferometers for gravitational-wave detection and provides a
measure of when macroscopic entanglement can be observed in the presence of
realistic decoherence processes
Negative optical inertia for enhancing the sensitivity of future gravitational-wave detectors
We consider enhancing the sensitivity of future gravitational-wave detectors
by using double optical spring. When the power, detuning and bandwidth of the
two carriers are chosen appropriately, the effect of the double optical spring
can be described as a "negative inertia", which cancels the positive inertia of
the test masses and thus increases their response to gravitational waves. This
allows us to surpass the free-mass Standard Quantum Limit (SQL) over a broad
frequency band, through signal amplification, rather than noise cancelation,
which has been the case for all broadband SQL-beating schemes so far considered
for gravitational-wave detectors. The merit of such signal amplification
schemes lies in the fact that they are less susceptible to optical losses than
noise cancelation schemes. We show that it is feasible to demonstrate such an
effect with the {\it Gingin High Optical Power Test Facility}, and it can
eventually be implemented in future advanced GW detectors.Comment: 7 pages, 3 figure
Quantum Enhancement of the Zero-Area Sagnac Interferometer Topology for Gravitational Wave Detection
Only a few years ago, it was realized that the zero-area Sagnac
interferometer topology is able to perform quantum nondemolition measurements
of position changes of a mechanical oscillator. Here, we experimentally show
that such an interferometer can also be efficiently enhanced by squeezed light.
We achieved a nonclassical sensitivity improvement of up to 8.2 dB, limited by
optical loss inside our interferometer. Measurements performed directly on our
squeezed-light laser output revealed squeezing of 12.7 dB. We show that the
sensitivity of a squeezed-light enhanced Sagnac interferometer can surpass the
standard quantum limit for a broad spectrum of signal frequencies without the
need for filter cavities as required for Michelson interferometers. The Sagnac
topology is therefore a powerful option for future gravitational-wave
detectors, such as the Einstein Telescope, whose design is currently being
studied.Comment: 4 pages, 4 figure
Noncommutative Moduli for Multi-Instantons
There exists a recursive algorithm for constructing BPST-type
multi-instantons on commutative R^4. When deformed noncommutatively, however,
it becomes difficult to write down non-singular instanton configurations with
topological charge greater than one in explicit form. We circumvent this
difficulty by allowing for the translational instanton moduli to become
noncommutative as well. This makes possible the ADHM construction of 't Hooft
multi-instanton solutions with everywhere self-dual field strengths on
noncommutative R^4.Comment: 1+9 pages; v2: reference added, published versio
Achieving ground state and enhancing entanglement by recovering information
For cavity-assisted optomechanical cooling experiments, it has been shown in
the literature that the cavity bandwidth needs to be smaller than the
mechanical frequency in order to achieve the quantum ground state of the
mechanical oscillator, which is the so-called resolved-sideband or good-cavity
limit. We provide a new but physically equivalent insight into the origin of
such a limit: that is information loss due to a finite cavity bandwidth. With
an optimal feedback control to recover those information, we can surpass the
resolved-sideband limit and achieve the quantum ground state. Interestingly,
recovering those information can also significantly enhance the optomechanical
entanglement. Especially when the environmental temperature is high, the
entanglement will either exist or vanish critically depending on whether
information is recovered or not, which is a vivid example of a quantum eraser.Comment: 9 figures, 18 page