Historical research guide · 0540 · 2004
Design of a Quantum Source of High-Frequency Gravitational Waves (HFGW) and Test Methodology
Giorgio Fontana
In one minute
Giorgio Fontana asks a plain question: a laser makes coherent light by stimulating identical atoms to drop between two energy levels, so what material would do the same for gravity? His answer is a superconductor. Quantum mechanics forbids photon emission on certain transitions — the ones where the orbital quantum number changes by two — and those are exactly the transitions that can emit a graviton instead. Fontana names a candidate material: an orthorhombic cuprate high-temperature superconductor, in which the s-wave and d-wave Cooper-pair condensates serve as the two levels, with an energy gap that puts the emitted wave near 1.3 terahertz. Because the pairs share a single macroscopic wavefunction the emission adds coherently, and the rate rises with the square of the number of pairs — which is what turns a hopeless single-particle probability into a device. The rest of the paper is engineering: crystal growth, a Josephson junction to pump it electrically, a capacitor bank for 100-kiloamp pulses, a curved geometry that focuses the waves, and how to detect the output.
Connection
Chapter 11 is where superconductors stop being a curiosity and start being gravitational hardware, and this is the most complete build sheet in that line: named material, named crystal orientation, named drive current, named frequency. Chapter 4 needs a source before any of its metrics can be engineered, and a coherent terahertz gravitational-wave emitter is the piece that a curvature-shaping craft would be built around.
From the source
Transitions in which the orbital quantum number changes by two and the total angular momentum changes by zero or two are gravitational quadrupole transitions: photon emission is forbidden and graviton emission is allowed, so a quantum system engineered to sit on such a transition radiates through the gravitational channel instead of the electromagnetic one.Section ’The HTSC GASER’, first paragraph, following Halpern 1964 and Ford 1982
For matrix elements of equal structure the ratio of graviton to photon transition probability is of order 1.6 times ten to the minus thirty-six for the proton and 4.8 times ten to the minus forty-three for the electron, so a workable source has to recover that shortfall through coherence and stimulated emission rather than through raw drive power.Section ’The HTSC GASER’, second paragraph
The proposed active material is an orthorhombic cuprate high-temperature superconductor whose s-wave and d-wave Cooper-pair condensates supply the two levels; the direct transition between them is purely gravitational, and the measured s-wave to d-wave gap in BSCCO puts the emitted frequency at about 1.3 terahertz.Section ’The HTSC GASER’, the five material requirements and the two paragraphs that follow them
Because the condensate is wavefunction-coherent, the graviton emission probability scales as the square of the number of Cooper pairs taking part; at pair densities of order ten to the twentieth per cubic centimetre the emission becomes interesting for a crystal volume of a few cubic centimetres, and the device can be pumped electrically by injecting s-wave pairs through a Josephson junction from a low-temperature superconductor, giving an estimated 10 watts of gravitational wave power per square centimetre at a current density of 10 kiloamps per square centimetre.Section ’The HTSC GASER’, the emission-probability and pumping paragraphs
A prototype is specified end to end: a melt-textured or thin-film cuprate crystal with the c axis along the emission direction, a lead or magnesium-diboride junction, and a pulsed drive of about 10 microfarads and 0.1 microhenries charged to roughly 10 kilovolts for peak currents of order 100 kiloamps into a disc of about 100 square centimetres and 1 centimetre thickness.Sections ’Production techniques and materials’ and ’Experimental setup and driving electronics’, with Figure 2
Tiling the emitters on a spherical surface makes them act as a point source at the centre with a power-density gain of order the emitting area divided by the wavelength squared; Fontana estimates such a curved gaser could deposit about a millijoule of gravitational energy at the focus, enough to accelerate test masses, and proposes detection by a synchroresonance converter or by ordinary gravimeters and accelerometers read with lock-in techniques.Section ’Structure’ with Figure 1; Section ’Detection of HFGWs and expected results’
The way in
https://doi.org/10.1063/1.1649680How to cite it
Giorgio Fontana (2004) Design of a Quantum Source of High-Frequency Gravitational Waves (HFGW) and Test Methodology doi:10.1063/1.1649680