arXiv subjects

Farid Khalili

Publications and source records attributed to Farid Khalili.

7 recordsLinked to original sources

arXiv2026

Path-Degenerate Quantum Interferometry for Decoherence Mitigation in Gravitational-Wave Detectors

Optical decoherence degrades quantum correlations in squeezed states of light, severely limiting the quantum-nondemolition (QND) sensitivity of gravitational-wave detectors. Here, we propose the path-degenerate quantum interferometry scheme that obviates the need for entire optical subsystems---including additional filter cavities, auxiliary parametric amplifiers, and Faraday isolators---thereby drastically reducing spatial mode mismatches while inherently integrating variational output, a long-standing theoretical proposal to further deepen the QND regime. We experimentally demonstrate a core aspect of this scheme, achieving a shot-noise-preserving signal enhancement that directly counteracts the detrimental effects of readout loss. By delivering an improved signal-to-quantum-noise ratio solely through the consolidation and reduction of currently considered optical subsystems, our approach offers a highly optimized route toward enhanced quantum-noise reduction in upcoming LIGO upgrades and next-generation gravitational-wave observatories.

quant-ph↗

arXiv2026

Application of optical squeezing to microresonator based optical sensors

High-Q optical microresonators combine low losses and high optical energy concentration in a small effective mode volume, making them an attractive platform for optical sensors. While light is confined in the microresonator by total internal reflection, a portion of the optical field, known as the evanescent field, extends outside. This makes the mode's resonant frequency sensitive to changes in the surrounding environment. In this work, we explore the quantum sensitivity limits of this type of sensors. We show that using the intracavity squeezing of the light in the microresonator, it is possible to suppress the influence of the optical losses and cancel the undesirable self phase modulation effect, originating from the cubic non-linearity of the microresonators media. As a result, the sensitivity surpassing the shot noise limit can be achieved. An additional sensitivity gain can be obtained by preparing the input light in a squeezed quantum state.

quant-ph↗

arXiv2017

Overcoming the SQL in gravitational wave detectors using spin systems with negative effective mass

Quantum back action (QBA) of a measurement limits the precision of observation of the motion of a free mass. This profound effect dabbed the "Heisenberg microscope" in the early days of quantum mechanics, leads to the standard quantum limit (SQL) stemming from the balance between the measurement sensitivity and the QBA. Here we consider the measurement of motion of a free mass performed in a quantum reference frame with an effective negative mass which is not limited by QBA. As a result, the disturbance on the motion of a free mass can be measured beyond SQL. QBA-limited detection of motion for a free mass is extremely challenging, but there are devices where this effect is expected to play an essential role, namely, gravitational wave detectors (GWD) such as LIGO and VIRGO. Recent reports on observation of gravitational waves have opened new horizons in cosmology and astrophysics. Here we present a general idea and a detailed numerical analysis for QBA-evading measurement of the gravitational wave effect on the GWD mirrors which can be considered free masses under relevant conditions. The measurement is performed by two entangled beams of light probing the GWD and an auxiliary atomic spin ensemble, respectively. The latter plays a role of a free negative mass. We show that under realistic conditions the sensitivity of the GWD can be significantly increased over the entire frequency band of interest.

quant-ph↗

arXiv2017

Detection loss tolerant supersensitive phase measurement with an SU(1,1) interferometer

In an unseeded SU(1,1) interferometer composed of two cascaded degenerate parametric amplifiers, with direct detection at the output, we demonstrate a phase sensitivity overcoming the shot noise limit by 2.3 dB. The interferometer is strongly unbalanced, with the parametric gain of the second amplifier exceeding the gain of the first one by a factor of 2, which makes the scheme extremely tolerant to detection losses. We show that by increasing the gain of the second amplifier, the phase supersensitivity of the interferometer can be preserved even with detection losses as high as 80%. This finding can considerably improve the state-of-the-art interferometry, enable sub-shot-noise phase sensitivity in spectral ranges with inefficient detection, and allow extension to quantum imaging.

quant-ph↗

arXiv2016

Improving the phase super-sensitivity of squeezing-assisted interferometers by squeeze factor unbalancing

The sensitivity properties of an SU(1,1) interferometer made of two cascaded parametric amplifiers, as well as of an ordinary SU(2) interferometer preceded by a squeezer and followed by an anti-squeezer, are theoretically investigated. Several possible experimental configurations are considered, such as the absence or presence of a seed beam, direct or homodyne detection scheme. In all cases we formulate the optimal conditions to achieve phase super-sensitivity, meaning a sensitivity overcoming the shot-noise limit. We show that for a given gain of the first parametric amplifier, unbalancing the interferometer by increasing the gain of the second amplifier improves the interferometer properties. In particular, a broader super-sensitivity phase range and a better overall sensitivity can be achieved by gain unbalancing.

quant-ph↗

arXiv2010

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.

gr-qc↗

arXiv2010

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.

quant-ph↗