Detecting high-frequency gravitational waves with optically-levitated sensors (1207.5320v2)

Abstract: We propose a tunable resonant sensor to detect gravitational waves in the frequency range of 50-300 kHz using optically trapped and cooled dielectric microspheres or micro-discs. The technique we describe can exceed the sensitivity of laser-based gravitational wave observatories in this frequency range, using an instrument of only a few percent of their size. Such a device extends the search volume for gravitational wave sources above 100 kHz by 1 to 3 orders of magnitude, and could detect monochromatic gravitational radiation from the annihilation of QCD axions in the cloud they form around stellar mass black holes within our galaxy due to the superradiance effect.

• The paper presents an innovative optically-levitated sensor technique targeting gravitational waves between 50–300 kHz.
• It uses resonant detection with dielectric particles in optical traps to achieve a sensitivity boost compared to conventional methods.
• The study highlights potential detection of monochromatic waves from axion annihilations near stellar mass black holes, expanding search volume significantly.

Detecting High-Frequency Gravitational Waves with Optically-Levitated Sensors

The paper authored by Asimina Arvanitaki and Andrew A. Geraci presents a method for detecting gravitational waves (GWs) at high frequencies, specifically within the range of 50 -- 300 kHz. This innovative approach employs optically trapped and cooled dielectric sensors, such as microspheres or microdiscs, to achieve sensitivity enhancements over conventional laser-based gravitational wave observatories in this frequency range, while significantly reducing the instrument size. This methodology potentially increases the search volume for gravitational wave sources between 100 kHz and 300 kHz by up to three orders of magnitude. A particularly noteworthy application of this technique is its potential to detect monochromatic gravitational radiation from QCD axion annihilation around stellar mass black holes (BHs) in our galaxy.

Gravitational Wave Detection via Optically-Levitated Devices

The proposed detector leverages the high mechanical quality factors achievable with optically trapped dielectric particles in ultra-high vacuum conditions, where vibrational modes are well-isolated. This isolation facilitates the trapping and precision force measurement of the dielectric sensors to the quantum ground state. Unlike conventional gravitational wave detectors which are shot-noise limited, this apparatus measures forces on resonant, harmonically trapped sensors, enabling sensitivity improvements of over an order of magnitude in the targeted frequency band.

The configuration involves a dielectric object, either a nanosphere or microdisc, levitated in an optical cavity. Gravitational waves alter the sensor's equilibrium position in the optical trap. When the GW frequency matches the trap frequency, the sensor's displacement is resonantly enhanced, functioning analogously to a resonant-bar detector. The design includes specific experimental parameters, including a 100 m cavity length for microdiscs and high reflectivity finesse, facilitating advanced force sensitivity measurements.

Experimental Precision and Parameters

The researchers simulated the use of a silica nanosphere and microdisc within a specifically configurated optical cavity. The sensitivity to gravitational waves is determined primarily by the thermal motion of the sensor rather than photon shot noise, indicating a reliance on resonant detection techniques. Operational parameters, such as the cavity dimensions and laser properties, have been meticulously optimized to achieve a thermal noise-limited strain sensitivity of $h_{\rm{limit}}$. This formulation considers both heating and cooling dynamics within the system to maintain optimal experimental conditions.

Gravitational Wave Sources and Detection Potential

A crucial implication of the paper is the potential detection of gravitational waves generated by axion annihilations in the clouds surrounding stellar mass black holes. These events produce a coherent and monochromatic GW signal, distinguished by frequencies dictated by the axion's mass. The proposed setup is exquisitely sensitive to signals originating from the annihilation of axions associated with the fundamental QCD theory.

A significant detection prospect arises when considering the existence of numerous black holes within our galaxy, with the GW emission from axion condensates potentially observable over extended periods. Given the axion's hypothetical role in addressing the strong CP problem in QCD, confirming such gravitational wave emissions could provide extraordinary insights into both black hole physics and fundamental particle interactions.

Conclusion and Future Research Directions

This paper delineates a compelling strategy for extending the capabilities of gravitational wave detectors to higher frequencies, which have been previously challenging to explore. The authors outline the infrastructure and technical requirements necessary to probe these frequency regimes with enhanced sensitivity and reduced noise interference.

Future work could extend this methodology by exploring longer cavity lengths or more complex arrays of traps to cover a broader frequency spectrum simultaneously. As gravitational wave astronomy continues to develop, the integration of these high-frequency observations could vastly enrich our understanding of astrophysical processes and fundamental physics. Additionally, efforts could be directed towards refining the detection techniques to elevate sensitivity and further mitigate recoil and environmental noise effects.

This research opens new avenues for gravitational wave studies and stands to propel our capabilities in detecting and analyzing phenomena from the broader cosmic landscape, including the elusive axion interactions. The potential of such detections offers promising insights into both astrophysical and theoretical physics domains.