675 research outputs found
Coherent Cancellation of Backaction Noise in optomechanical Force Measurements
Optomechanical detectors have reached the standard quantum limit in position
and force sensing where measurement backaction noise starts to be the limiting
factor for the sensitivity. A strategy to circumvent measurement backaction,
and surpass the standard quantum limit, has been suggested by M. Tsang and C.
Caves in Phys. Rev. Lett. 105 123601 (2010). We provide a detailed analysis of
this method and assess its benefits, requirements, and limitations. We conclude
that a proof-of-principle demonstration based on a micro-optomechanical system
is demanding, but possible. However, for parameters relevant to gravitational
wave detectors the requirements for backaction evasion appear to be
prohibitive.Comment: 9 pages, 6 figure
Laser power stabilization for second-generation gravitational wave detectors
We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10−9 Hz−1/2 at 10 Hz and 3.5×10−9 Hz−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector
Utilizing weak pump depletion to stabilize squeezed vacuum states
We propose and demonstrate a pump-phase locking technique that makes use of
weak pump depletion (WPD) - an unavoidable effect that is usually neglected -
in a sub-threshold optical parametric oscillator (OPO). We show that the phase
difference between seed and pump beam is imprinted on both light fields by the
non-linear interaction in the crystal and can be read out without disturbing
the squeezed output. Our new locking technique allows for the first
experimental realization of a pump-phase lock by reading out the pre-existing
phase information in the pump field. There is no degradation of the detected
squeezed states required to implement this scheme.Comment: 11 pages, 7 figure
Multiplexed communication over a high-speed quantum channel
In quantum information systems it is of particular interest to consider the
best way in which to use the non-classical resources consumed by that system.
Quantum communication protocols are integral to quantum information systems and
are amongst the most promising near-term applications of quantum information
science. Here we show that a multiplexed, digital quantum communications system
supported by comb of vacuum squeezing has a greater channel capacity per photon
than a source of broadband squeezing with the same analogue bandwidth. We
report on the time-resolved, simultaneous observation of the first dozen teeth
in a 2.4 GHz comb of vacuum squeezing produced by a sub-threshold OPO, as
required for such a quantum communications channel. We also demonstrate
multiplexed communication on that channel
Homodyne locking of a squeezer
We report on the successful implementation of a new approach to locking the
frequencies of an OPO-based squeezed-vacuum source and its driving laser. The
technique allows the simultaneous measurement of the phase-shifts induced by a
cavity, which may be used for the purposes of frequency-locking, as well as the
simultaneous measurement of the sub-quantum-noise-limited (sub-QNL) phase
quadrature output of the OPO. The homodyne locking technique is cheap, easy to
implement and has the distinct advantage that subsequent homodyne measurements
are automatically phase-locked. The homodyne locking technique is also unique
in that it is a sub-QNL frequency discriminator.Comment: Accepted to Optics Letter
The GEO 600 laser system
Interferometric gravitational wave detectors require high optical power, single frequency lasers with very good beam quality and high amplitude and frequency stability as well as high long-term reliability as input light source. For GEO 600 a laser system with these properties is realized by a stable planar, longitudinally pumped 12 W Nd:YAG rod laser which is injection-locked to a monolithic 800 mW Nd:YAG non-planar ring oscillator. Frequency control signals from the mode cleaners are fed to the actuators of the non-planar ring oscillator which determines the frequency stability of the system. The system power stabilization acts on the slave laser pump diodes which have the largest influence on the output power. In order to gain more output power, a combined Nd:YAGNd:YVO4 system is scaled to more than 22 W
All-optical coherent quantum-noise cancellation in cascaded optomechanical systems
Coherent quantum noise cancellation (CQNC) can be used in optomechanical
sensors to surpass the standard quantum limit (SQL). In this paper, we
investigate an optomechanical force sensor that uses the CQNC strategy by
cascading the optomechanical system with an all-optical effective negative mass
oscillator. Specifically, we analyze matching conditions, losses and compare
the two possible arrangements in which either the optomechanical or the
negative mass system couples first to light. While both of these orderings
yield a sub-SQL performance, we find that placing the effective negative mass
oscillator before the optomechanical sensor will always be advantageous for
realistic parameters. The modular design of the cascaded scheme allows for
better control of the sub-systems by avoiding undesirable coupling between
system components, while maintaining similar performance to the integrated
configuration proposed earlier. We conclude our work with a case study of a
micro-optomechanical implementation.Comment: 9 pages, 6 figures, Appendix A and
Stabilized High Power Laser for Advanced Gravitational Wave Detectors
Second generation gravitational wave detectors require high power lasers with several 100W of output power and with very low temporal and spatial fluctuations. In this paper we discuss possible setups to achieve high laser power and describe a 200W prestabilized laser system (PSL). The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described. Special emphasis will be given to the most demanding power stabilization requiremets and new results (RIN ≤ 4×10-9/surdHz) will be presented
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