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arXiv:2504.18111 · npj Quantum Information

Teleportation-based speed meter for precision measurement

Yohei Nishino, James W. Gardner, Yanbei Chen, Kentaro Somiya

Published Oct 22, 2025• 5 citations
arXivHTMLPDF

Abstract

We propose a quantum teleportation-based speed meter for interferometric displacement sensing. The primary motivation is to transform a conventional position-sensing interferometer into a quantum non-demolition speed measurement device, without modifying its fundamental optical configuration. Two equivalent implementations are presented: an online approach that uses real-time displacement operation and an offline approach that relies on post-processing. Both implementations reduce quantum radiation pressure noise and surpass the standard quantum limit of measuring displacement, and they can be applied to a wide range of interferometer configurations. We discuss potential applications to gravitational-wave detectors, where our scheme enhances low-frequency sensitivity without requiring modifications to the core optics of a conventional Michelson interferometer (e.g., substrate or coating properties). This approach offers a new path to back-action evasion enabled by quantum entanglement.

DOI
10.1038/s41534-025-01107-9

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In the quest to develop viable designs for third-generation optical interferometric gravitational-wave detectors (e.g. LIGO-III and EURO), one strategy is to monitor the relative momentum or speed of the test-mass mirrors rather than monitoring their relative position. This paper describes and analyzes the most straightforward design for a speed meter interferometer that accomplishes this---a design (due to Braginsky, Gorodetsky, Khalili and Thorne) that is analogous to a microwave-cavity speed meter conceived by Braginsky and Khalili. A mathematical mapping between the microwave speed meter and the optical interferometric speed meter is developed and is used to show [in accord with the speed being a quantum nondemolition observable] that in principle the interferometric speed meter can beat the gravitational-wave standard quantum limit (SQL) by an arbitrarily large amount, over an arbitrarily wide range of frequencies, and can do so without the use of squeezed vacuum or any auxiliary filter cavities at the interferometer's input or output. However, in practice, to reach or beat the SQL, this specific speed meter requires exorbitantly high input light power. The physical reason for this is explored, along with other issues such as constraints on performance due to optical dissipation. This analysis forms a foundation for ongoing attempts to develop a more practical variant of an interferometric speed meter and to combine the speed meter concept with other ideas to yield a promising LIGO-III/EURO interferometer design that entails low laser power.

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We propose a quantum teleportation-based speed meter for interferometric displacement sensing. The primary motivation is to transform a conventional position-sensing interferometer into a quantum non-demolition speed measurement device, without modifying its fundamental optical configuration. Two equivalent implementations are presented: an online approach that uses real-time displacement operation and an offline approach that relies on post-processing. Both implementations reduce quantum radiation pressure noise and surpass the standard quantum limit of measuring displacement, and they can be applied to a wide range of interferometer configurations. We discuss potential applications to gravitational-wave detectors, where our scheme enhances low-frequency sensitivity without requiring modifications to the core optics of a conventional Michelson interferometer (e.g., substrate or coating properties). This approach offers a new path to back-action evasion enabled by quantum entanglement.
Abstract We propose several quantum noise reduction schemes for gravitational-wave detectors based on quantum teleportation. Gravitational-wave detectors, as highly precise displacement-measurement devices, are ultimately limited by quantum shot noise and radiation pressure noise. The trade-off between these two noise sources imposes the so-called standard quantum limit (SQL), as a natural consequence of Heisenberg’s uncertainty principle. Numerous schemes to enhance the quantum noise- limited sensitivity beyond the SQL have been proposed, some of which require nontrivial modifications to the basic Michelson configuration of the detectors. Recently, it has been found that the principles of quantum teleportation can solve this issue; the detector’s sensitivity can be enhanced beyond the SQL at minimal cost via parallel processing, which is a key concept in quantum information processing. We theoretically demonstrate ways to implement quantum teleportation in (1) frequency-dependent squeezing [1] and (2) quantum speed measurement [2], without requiring additional infrastructure or the manufacture of optics. We conclude that these ideas can be viable candidates for future detectors.
Abstract The recent discovery of gravitational waves (GW) by Advanced LIGO (Laser Interferometric Gravitational-wave Observatory) has impressively launched the novel field of gravitational astronomy and allowed us to glimpse exciting objects about which we could previously only speculate. Further sensitivity improvements at the low-frequency end of the detection band of future GW observatories must rely on quantum non-demolition (QND) methods to suppress fundamental quantum fluctuations of the light fields used to readout the GW signal. Here we present a novel concept of how to turn a conventional Michelson interferometer into a QND speed-meter interferometer with coherently suppressed quantum back-action noise. We use two orthogonal polarizations of light and an optical circulator to couple them. We carry out a detailed analysis of how imperfections and optical loss influence the achievable sensitivity. We find that the proposed configuration significantly enhances the low-frequency sensitivity and increases the observable event rate of binary black-hole coalescences in the range of 102−103 M⊙10^2 - 10^3\,M_ \odot102−103M⊙​ 1 0 2 - 1 0 3 M ⊙ by a factor of up to ~300.
Sensitivity of gravitational-wave detectors (GWDs) is constrained at low frequencies by quantum radiation-pressure noise, a manifestation of the measurement's back action. One strategy to mitigate this back action involves employing variational readout, which entails cross-correlating the measurement shot noise with radiation-pressure noise. Prior research has demonstrated that variational readout in GWDs can be accomplished through the use of a filter cavity. However, current gravitational-wave detectors necessitate filter cavity lengths on the order of ∼100\sim 100∼100 meters, with future detectors anticipated to reach lengths of a few kilometers. This paper introduces a novel approach to variational readout utilizing principle of quantum teleportation, which eliminates the need for a filter cavity. *This document will not be published any journals, since it turned out to be not very useful for the real detectors. The main reason is that one does not need the EPR entanglement to obtain the same result, which does not even shows true variational readout. In other words, both schemes do not exceed the EPR squeezing. Nevertheless this document will be uploaded to stimulate discussions how to realize "true" back action evasion, such as variational readout or speed meter, via quantum entanglement.
We propose a new implementation of a quantum speed meter QND measurement scheme. It employs two independent optical readouts of the interferometer test masses with different values of the bandwidths and of the optical circulating power, whose outputs have to be combined by an additional beamsplitter. Signals at the two outputs of the beamsplitter are proportional to the position and the velocity of the test masses, respectively. The influence of the position meter-like back action force associated with the position signal can be cancelled using the EPR approach by measuring the amplitude quadrature of the beamsplitter common output. • This is an article for the Special Issue in memory of V.B. Braginsky. • We propose a novel and arguably the simplest scheme of a speed meter interferometer. • Speed meters curb quantum noise at low frequencies, boosting the SNR for GW sources. • Combination of readouts of two detectors with distinct bandwidths yields speed signal. • No significant changes of the current GWD infrastructure is necessary for our scheme.
In the quest to develop viable designs for third-generation optical interferometric gravitational-wave detectors (e.g., LIGO-III and EURO), one strategy is to monitor the relative momentum or speed of the test-mass mirrors, rather than monitoring their relative position. A previous paper analyzed a straightforward but impractical design for a speed-meter interferometer that accomplishes this. This paper describes some practical variants of speed-meter interferometers. Like the original interferometric speed meter, these designs in principle can beat the gravitational-wave standard quantum limit (SQL) by an arbitrarily large amount, over an arbitrarily wide range of frequencies. These variants essentially consist of a Michelson interferometer plus an extra ``sloshing'' cavity that sends the signal back into the interferometer with opposite phase shift, thereby cancelling the position information and leaving a net phase shift proportional to the relative velocity. In practice, the sensitivity of these variants will be limited by the maximum light power Wcirc{W}_{\mathrm{circ}}Wcirc​ circulating in the arm cavities that the mirrors can support and by the leakage of vacuum into the optical train at dissipation points. In the absence of dissipation and with squeezed vacuum (power squeeze factor ${e}^{\ensuremath{-}2R}\ensuremath{\simeq}0.1)$ inserted into the output port so as to keep the circulating power down, the SQL can be beat by ${h/h}_{\mathrm{SQL}}\ensuremath{\sim}\sqrt{{W}_{\mathrm{circ}}^{\mathrm{SQL}}{e}^{\ensuremath{-}2R}{/W}_{\mathrm{circ}}}$ at all frequencies below some chosen ${f}_{\mathrm{opt}}\ensuremath{\simeq}100\mathrm{Hz}.$ Here ${W}_{\mathrm{circ}}^{\mathrm{SQL}}\ensuremath{\simeq}800\mathrm{kW}{(f}_{\mathrm{opt}}/100\mathrm{}\mathrm{Hz}{)}^{3}$ is the power required to reach the SQL in the absence of squeezing. (However, as the power increases in this expression, the speed meter becomes more narrow band; additional power and reoptimization of some parameters are required to maintain the wide band. See Sec. III B.) Estimates are given of the amount by which vacuum leakage at dissipation points will debilitate this sensitivity (see Fig. 12); these losses are 10% or less over most of the frequency range of interest $(f\ensuremath{\gtrsim}10\mathrm{Hz}).$ The sensitivity can be improved, particularly at high freqencies, by using frequency-dependent homodyne detection, which unfortunately requires two 4-km-long filter cavities (see Fig. 4).
In the quest to develop viable designs for third-generation optical interferometric gravitational-wave detectors (e.g. LIGO-III and EURO), one strategy is to monitor the relative momentum or speed of the test-mass mirrors rather than monitoring their relative position. This paper describes and analyzes the most straightforward design for a speed meter interferometer that accomplishes this---a design (due to Braginsky, Gorodetsky, Khalili and Thorne) that is analogous to a microwave-cavity speed meter conceived by Braginsky and Khalili. A mathematical mapping between the microwave speed meter and the optical interferometric speed meter is developed and is used to show [in accord with the speed being a quantum nondemolition observable] that in principle the interferometric speed meter can beat the gravitational-wave standard quantum limit (SQL) by an arbitrarily large amount, over an arbitrarily wide range of frequencies, and can do so without the use of squeezed vacuum or any auxiliary filter cavities at the interferometer's input or output. However, in practice, to reach or beat the SQL, this specific speed meter requires exorbitantly high input light power. The physical reason for this is explored, along with other issues such as constraints on performance due to optical dissipation. This analysis forms a foundation for ongoing attempts to develop a more practical variant of an interferometric speed meter and to combine the speed meter concept with other ideas to yield a promising LIGO-III/EURO interferometer design that entails low laser power.