961 research outputs found
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
A squeezed state source using radiation pressure induced rigidity
We propose an experiment to extract ponderomotive squeezing from an
interferometer with high circulating power and low mass mirrors. In this
interferometer, optical resonances of the arm cavities are detuned from the
laser frequency, creating a mechanical rigidity that dramatically suppresses
displacement noise. After taking into account imperfection of optical elements,
laser noise, and other technical noise consistent with existing laser and
optical technologies and typical laboratory environments, we expect the output
light from the interferometer to have measurable squeezing of ~5 dB, with a
frequency-independent squeeze angle for frequencies below 1 kHz. This squeeze
source is well suited for injection into a gravitational-wave interferometer,
leading to improved sensitivity from reduction in the quantum noise.
Furthermore, this design provides an experimental test of quantum-limited
radiation pressure effects, which have not previously been tested.Comment: 15 pages, 6 figures, submitted to Phys. Rev.
Design of microresonators to minimize thermal noise below the standard quantum limit
Microfabricated resonators play a crucial role in the development of quantum measurement, including future gravitational wave detectors. We use a micro-genetic algorithm and a finite element method to design a microresonator whose geometry is optimized to maximize the sub-Standard Quantum Limit (SQL) performance including lower thermal noise (TN) below the SQL, a broader sub-SQL region, and a sub-SQL region at lower frequencies. For the proposed design, we study the effects of different geometries of the mirror pad and cantilever microresonator on sub-SQL performance. We find that the maximum ratio of SQL to TN is increased, its frequency is decreased, and the sub-SQL range is increased by increasing the length of the microresonator cantilever, increasing the radius of the mirror pad, decreasing the width of the microresonator cantilever, and shifting the laser beam location from the mirror center. We also find that there exists a trade-off between the maximum ratio of SQL to TN and the sub-SQL bandwidth. The performance of this designed microresonator will allow it to serve as a test-bed for quantum non-demolition measurements and to open new regimes of precision measurement that are relevant for many practical sensing applications, including advanced gravitational wave detectors
A microchip optomechanical accelerometer
The monitoring of accelerations is essential for a variety of applications
ranging from inertial navigation to consumer electronics. The basic operation
principle of an accelerometer is to measure the displacement of a flexibly
mounted test mass; sensitive displacement measurement can be realized using
capacitive, piezo-electric, tunnel-current, or optical methods. While optical
readout provides superior displacement resolution and resilience to
electromagnetic interference, current optical accelerometers either do not
allow for chip-scale integration or require bulky test masses. Here we
demonstrate an optomechanical accelerometer that employs ultra-sensitive
all-optical displacement read-out using a planar photonic crystal cavity
monolithically integrated with a nano-tethered test mass of high mechanical
Q-factor. This device architecture allows for full on-chip integration and
achieves a broadband acceleration resolution of 10 \mu g/rt-Hz, a bandwidth
greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical
power requirements. Moreover, the nano-gram test masses used here allow for
optomechanical back-action in the form of cooling or the optical spring effect,
setting the stage for a new class of motional sensors.Comment: 16 pages, 9 figure
Broadband reduction of quantum radiation pressure noise via squeezed light injection
The Heisenberg uncertainty principle states that the position of an object cannot be known with infinite precision, as the momentum of the object would then be totally uncertain. This momentum uncertainty then leads to position uncertainty in future measurements. When continuously measuring the position of an object, this quantum effect, known as back-action, limits the achievable precision1,2. In audio-band, interferometer-type gravitational-wave detectors, this back-action effect manifests as quantum radiation pressure noise (QRPN) and will ultimately (but does not yet) limit sensitivity3. Here, we present the use of a quantum engineered state of light to directly manipulate this quantum back-action in a system where it dominates the sensitivity in the 10–50 kHz range. We observe a reduction of 1.2 dB in the quantum back-action noise. This experiment is a crucial step in realizing QRPN reduction for future interferometric gravitational-wave detectors and improving their sensitivity
Resolved Sideband Cooling of a Micromechanical Oscillator
Micro- and nanoscale opto-mechanical systems provide radiation pressure
coupling of optical and mechanical degree of freedom and are actively pursued
for their ability to explore quantum mechanical phenomena of macroscopic
objects. Many of these investigations require preparation of the mechanical
system in or close to its quantum ground state. Remarkable progress in ground
state cooling has been achieved for trapped ions and atoms confined in optical
lattices. Imperative to this progress has been the technique of resolved
sideband cooling, which allows overcoming the inherent temperature limit of
Doppler cooling and necessitates a harmonic trapping frequency which exceeds
the atomic species' transition rate. The recent advent of cavity back-action
cooling of mechanical oscillators by radiation pressure has followed a similar
path with Doppler-type cooling being demonstrated, but lacking inherently the
ability to attain ground state cooling as recently predicted. Here we
demonstrate for the first time resolved sideband cooling of a mechanical
oscillator. By pumping the first lower sideband of an optical microcavity,
whose decay rate is more than twenty times smaller than the eigen-frequency of
the associated mechanical oscillator, cooling rates above 1.5 MHz are attained.
Direct spectroscopy of the motional sidebands reveals 40-fold suppression of
motional increasing processes, which could enable reaching phonon occupancies
well below unity (<0.03). Elemental demonstration of resolved sideband cooling
as reported here should find widespread use in opto-mechanical cooling
experiments. Apart from ground state cooling, this regime allows realization of
motion measurement with an accuracy exceeding the standard quantum limit.Comment: 13 pages, 5 figure
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