Nuclear singlet state in diamond for overcoming the standard quantum limit in gravitational wave detectors

The sensitivity of the next-generation gravitational-wave detectors (GWD) are critically limited by the quantum fluctuations of light. The major sources of such noises are shot noise and optomechanical back action noise (BAN).

The improvement of sensitivity can be achieved by back-action evading (BAE) measurements, which allows overcoming the standard quantum limit.

By trading off between shot and BAN, recently a promising scheme has been proposed which involves another auxiliary system, consisting of an atomic spin ensemble with negative effective mass that can suppress both the noises. The measurement is performed by two entangled beams of light probing the GWD and the spin ensemble.

However, the approach exhibits three major implementational issues to focus on, which I have discovered by recent calculations.

Firstly, I study how the sensitivity of the GWD is dependent and what the constraints introduced by the entanglement measures between subsystems.

Secondly, I come with a novel approach for the BAE by using a nuclear singlet state of carbon in diamond which works at very low NMR frequencies and bandwidth aiming to avoid the discrepancies of the match between the frequencies and linewidths of the spin and the mechanical oscillators.

In this aspect, I propose using a novel type readout of electron spin of NV centers, used as a non-perturbing ancilla of the nuclear spin-singlet.

Finally, based on the parameters obtained from ongoing E-Test project, where a low thermal noise mechanical oscillator is being built up, I will theoretically investigate if the nuclear singlet state can match the frequency and bandwidth of rational parameters of the oscillator and whether it can be implemented for the BAE measurement.

I will study the role played by the input squeezing parameters, and how to engineer the frequency range of noise suppression of the output. The proposal entitles advanced hands-on training on experimental setups and profounding my background in GWD.