Table 1 Selected system parameters for various GW sources for the detection of single gravitons through stimulated absorption

GW source	GW170817 (NS–NS merger)	GW170817 (NS–NS merger)	GW170608 (BH–BH merger)	GW150914 (BH–BH merger)	J1301+0833 (black-widow pulsar)	J1748-2446ad (fast-spinning pulsar)	A0620-00 (BH Superradiance)	Primordial (rare BH–BH merger)
\({f}=\frac{\omega }{2\pi }\)	100 Hz	150 Hz	175 Hz	200 Hz	1085 Hz	1433 Hz	33 kHz	5.5 MHz
h₀(f)	2 × 10⁻²²	2 × 10⁻²²	2 × 10⁻²²	10⁻²¹	<10⁻²⁵	<10⁻²⁵	3 × 10⁻²¹	10⁻¹⁶
M_c	1.19M_⊙	1.19M_⊙	7.9M_⊙	28.6M_⊙	Continuous	Continuous	Continuous	5 × 10⁻⁴M_⊙
Material	Beryllium	Aluminum	Niobium	CuAl6%	Niobium	Superfluid He-4	Sapphire	Quartz
ν_o	13 km/s	5.4 km/s	5 km/s	4.1 km/s	5 km/s	238 m/s	10 km/s	6.3 km/s
T	1 mK	1 mK	1 mK	1 mK	0.1 μK	0.1 μK	0.6 K	0.6 mK
Q-factor	10¹⁰	10¹⁰	10¹⁰	10¹⁰	10¹⁰	10¹³	10¹⁰	10¹⁰
M	~15 kg	~250 kg	~9 t	~6 t	>52 t	>20 t	~100 kg	~10 g

Here, f is the resonant frequency, h₀(f) the GW amplitude at that frequency, M_c the chirp mass of the GW source in terms of solar mass M_⊙ where applicable, v₀ the speed of sound, T the environmental temperature, Q the mechanical Q-factor of the mode and M the mass of the required resonator. Experiments in the LIGO band would focus on transient GWs (first four columns) and could correlate events to LIGO detections of black hole (BH) or neutron star (NS) mergers. Nearby NS mergers³² with low chirp mass M_c provide the best candidates, shown in the first two columns. For higher frequencies, the sources are of a speculative nature, such as continuous GWs from pulsars at kHz frequencies^34,36, and speculative sources due to new physics in the ultra-high frequency range³⁷. The last column corresponds to a possible rare event of such a hypothetical source⁴⁰. For continuous sources, the temperature is calculated which ensures the graviton absorption rate given in Eq. (5) is larger than the rate of thermal phonons for the given Q-factor and frequency. For transient sources, the temperature is calculated such that the thermal-phonon rate integrated over a 40 s observation-window yields an excitation probability lower than P ≈ 0.3.

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