114 research outputs found
Towards the Design of Gravitational-Wave Detectors for Probing Neutron-Star Physics
The gravitational waveform of merging binary neutron stars encodes
information about extreme states of matter. Probing these gravitational
emissions requires the gravitational-wave detectors to have high sensitivity
above 1 kHz. Fortunately for current advanced detectors, there is a sizeable
gap between the quantum-limited sensitivity and the classical noise at high
frequencies. Here we propose a detector design that closes such a gap by
reducing the high-frequency quantum noise with an active optomechanical filter,
frequency-dependent squeezing, and high optical power. The resulting noise
level from 1 kHz to 4 kHz approaches the current facility limit and is a factor
of 20 to 30 below the design of existing advanced detectors. This will allow
for precision measurements of (i) the post-merger signal of the binary neutron
star, (ii) late-time inspiral, merger, and ringdown of low-mass black
hole-neutron star systems, and possible detection of (iii) high-frequency modes
during supernovae explosions. This design tries to maximize the science return
of current facilities by achieving a sensitive frequency band that is
complementary to the longer-baseline third-generation detectors: the10 km
Einstein Telescope, and 40 km Cosmic Explorer. We have highlighted the main
technical challenges towards realizing the design, which requires dedicated
research programs. If demonstrated in current facilities, the techniques can be
transferred to new facilities with longer baselines.Comment: 14 pages, 15 figures, published versio
Non-adiabatic elimination of auxiliary modes in continuous quantum measurements
When measuring a complex quantum system, we are often interested in only a
few degrees of freedom-the plant, while the rest of them are collected as
auxiliary modes-the bath. The bath can have finite memory (non-Markovian), and
simply ignoring its dynamics, i.e., adiabatically eliminating it, will prevent
us from predicting the true quantum behavior of the plant. We generalize the
technique introduced by Strunz et. al. [Phys. Rev. Lett 82, 1801 (1999)], and
develop a formalism that allows us to eliminate the bath non-adiabatically in
continuous quantum measurements, and obtain a non-Markovian stochastic master
equation for the plant which we focus on. We apply this formalism to three
interesting examples relevant to current experiments.Comment: a revised versio
Universal quantum entanglement between an oscillator and continuous fields
Quantum entanglement has been actively sought in optomechanical and electromechanical systems. The simplest system is a mechanical oscillator interacting with a coherent optical field, while the oscillator also suffers from thermal decoherence. With a rigorous functional analysis, we develop a mathematical framework for treating quantum entanglement that involves infinite degrees of freedom. We show that the quantum entanglement is always present between the oscillator and continuous optical field—even when the environmental temperature is high and the oscillator is highly classical. Such a universal entanglement is also shown to be able to survive more than one mechanical oscillation period if the characteristic frequency of the optomechanical interaction is larger than that of the thermal noise. In addition, we introduce effective optical modes that are ordered by the entanglement strength to better understand the entanglement structure, analogously to the energy spectrum of an atomic system. In particular, we derive the optical mode that is maximally entangled with the mechanical oscillator, which will be useful for future quantum computing and encoding information into mechanical degrees of freedom
General quantum constraints on detector noise in continuous linear measurements
In quantum sensing and metrology, an important class of measurement is the
continuous linear measurement, in which the detector is coupled to the system
of interest linearly and continuously in time. One key aspect involved is the
quantum noise of the detector, arising from quantum fluctuations in the
detector input and output. It determines how fast we acquire information about
the system and also influences the system evolution in terms of measurement
backaction. We therefore often categorize it as the so-called imprecision noise
and quantum backaction noise. There is a general Heisenberg-like uncertainty
relation that constrains the magnitude of and the correlation between these two
types of quantum noise. The main result of this paper is to show that, when the
detector becomes ideal, i.e., at the quantum limit with minimum uncertainty,
not only does the uncertainty relation takes the equal sign as expected, but
also there are two new equalities. This general result is illustrated by using
the typical cavity QED setup with the system being either a qubit or a
mechanical oscillator. Particularly, the dispersive readout of a qubit state,
and the measurement of mechanical motional sideband asymmetry are considered.Comment: journal accepted versio
Enhancing the bandwidth of gravitational-wave detectors with unstable optomechanical filters
For gravitational-wave interferometric detectors, there is a tradeoff between
the detector bandwidth and peak sensitivity when focusing on the shot noise
level. This has to do with the frequency-dependent propagation phase lag
(positive dispersion) of the signal. We consider embedding an active unstable
filter---a cavity-assisted optomechanical device operating in the instability
regime---inside the interferometer to compensate the phase, and using feedback
control to stabilize the entire system. We show that this scheme in principle
can enhance the bandwidth without sacrificing the peak sensitivity. However,
there is one practical difficulty for implementing it due to the thermal
fluctuation of the mechanical oscillator in the optomechanical filter, which
puts a very stringent requirement on the environmental temperature and the
mechanical quality factor.Comment: 5 pages and 6 figures. Comments are welcom
Quantum noise of white light cavity using double-pumped gain medium
Laser interferometric gravitational-wave detectors implement Fabry-Perot
cavities to increase their peak sensitivity. However, this is at cost of
reducing their detection bandwidth, which origins from the propagation phase
delay of the light. The "white-light-cavity" idea, first proposed by Wicht et
al. [Optics Communications 134, 431 (1997)], is to circumvent this limitation
by introducing anomalous dispersion, using double-pumped gain medium, to
compensate for such phase delay. In this article, starting from the Hamiltonian
of atom-light interaction, we apply the input-output formalism to evaluate the
quantum noise of the system. We find that apart from the additional noise
associated with the parametric amplification process noticed by others, the
stability condition for the entire system poses an additional constraint.
Through surveying the parameter regimes where the gain medium remains stable
(not lasing) and stationary, we find that there is no net enhancement of the
shot-noise limited sensitivity. Therefore, other gain mediums or different
parameter regimes shall be explored for realizing the white light cavity.Comment: 12 pages, 7 figure
Sensitivity of intracavity filtering schemes for detecting gravitational waves
We consider enhancing the sensitivity of future gravitational-wave detectors
by adding optical filters inside the signal-recycling cavity -- an intracavity
filtering scheme, which coherently feeds the sideband signal back to the
interferometer with a proper frequency-dependent phase. We study three cases of
such a scheme with different motivations: (i) the case of backaction noise
evasion, trying to cancel radiation-pressure noise with only one filter cavity
for a signal-recycled interferometer; (ii) the speed-meter case, similar to the
speed-meter scheme proposed by Purdue and Chen [Phys. Rev. D 66, 122004 (2002)]
but without the resonant-sideband-extraction mirror, and also relieves the
optical requirement on the sloshing mirror; (iii) the broadband detection case
with squeezed-light input, numerically optimized for a broadband sensitivity.Comment: 10 pages, 10 figure
Quantum-enhanced interferometry for axion searches
We propose an experiment to search for axions and axion-like-particles in the
galactic halo using quantum-enhanced interferometry. This proposal is related
to the previously reported ideas (Phys. Rev. D 98, 035021, Phys. Rev. Lett.
121, 161301, Phys. Rev. D 100, 023548) but searches for axions in the mass
range from eV up to eV using two coupled optical cavities.
We also show how to apply squeezed states of light to enhance the sensitivity
of the experiment similar to the gravitational-wave detectors. The proposed
experiment has a potential to be further scaled up to a multi-km long detector.
We show that such an instrument has a potential to set constrains of the
axion-photon coupling coefficient of GeV for axion
masses of eV or detect the signal
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