Demonstration of interferometer enhancement through Einstein–Podolsky–Rosen entanglement

Abstract

The sensitivity of laser interferometers used for the detection of gravitational waves (GWs) is limited by quantum noise of light. An improvement is given by light with squeezed quantum uncertainties, as employed in the GW detector GEO 600 since 2010. To achieve simultaneous noise reduction at all signal frequencies, however, the spectrum of squeezed states needs to be processed by 100 m-scale low-loss optical filter cavities in vacuum. Here, we report on the proof-ofprinciple of an interferometer setup that achieves the required processed squeezed spectrum by employing Einstein-Podolsky-Rosen (EPR) entangled states. Applied to GW detectors, the costintensive cavities would become obsolete, while the price to pay is a 3 dB quantum penalty.

Quantum sensing of open systems: Estimation of damping constants and temperature

“…δγ min /γ . (8) This expression shows that the uncertainty in γ has two contributions, the term ( N ) 2 in stemming from the initial variance in the bosonic number of the incoming probe and the remaining terms corresponding to the random transmission of the incoming bosons. It is clear that, in order to minimize (8), one must have ( N ) 2 in = 0, implying that the incoming bosons should be in a Fock state.…”

“…Through a generalization of the classical framework to quantum mechanics [3][4][5][6], it has been realized that quantum probes, prepared in states with features like squeezing and entanglement, help to increase the precision of the estimation, for the same amount of resources (which could be the number of atoms or photons used in the estimation). This has been relevant, for instance, for extending the coverage of gravitational-wave interferometers, with the use of squeezed light [5,7] or of entangled states [8], for increasing the magnetic sensitivity with spin squeezing [9], for optimal thermometry [10], for detecting weak electric fields with superpositions of Rydberg states [11], for achieving quantum-enhanced contrast and resolution in biological microscopy [12,13], and for superresolution of spatial separation and frequency [14]. Quantum sensing [15,16] involves the exploration of subtle quantum effects to increase the precision of parameter estimation.…”

Broadband quantum noise reduction in future long baseline gravitational-wave detectors via EPR entanglement

“…The corresponding required detuning and bandwidth for given Eq. (9) and ω s Ω, following a similar derivation as Refs. [8,19]:…”

“…These proposals require additional low-loss filter cavities. It was shown recently that an alternative approach to achieving frequencydependent squeezing without additional cavities is using EPRentangled signal and idler beams (different frequency components in conventional squeezed light source) [8], which has been demonstrated in proof-of-principle experiments [9,10]. In this paper, we present a systematic way of finding the working points for this broadband squeezing scheme in LBIs.…”

Resource reduction for simultaneous generation of two types of continuous variable nonclassical states

“…The optical parametric process has been proven as one of the most successful systems for nonclassical states generation, especially for the generation of high-level squeezed states [28][29][30][31], which has continually held the record for the largest amount of quantum noise reduction [32]. In such process, a high energy pump photon is converted into a pair of lower energy photons subject to energy conservation and the cavity resonance condition, via a second order nonlinear interaction [33][34][35][36][37][38][39][40]. The generation of a photon pair initiates a nonclassical correlation between the symmetric cavity modes along half the pump frequency.…”