A quantum Bell Test homodyne interferometer at ambient temperature for millimetre wave entangled photons

Salmon, Neil (2018) A quantum Bell Test homodyne interferometer at ambient temperature for millimetre wave entangled photons. Proceedings of SPIE, 10803. ISSN 0277-786X

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Abstract

This paper investigates the feasibility of operating a Bell Test for millimetre wave entangled photons using ambient temperature instrumentation, raising the question as to whether this can be done in a regime where the photon energy (hf/e ~ 0.06 milli-eV at 10 GHz) is far smaller than the thermal energy (kT/e ~ 25 milli-eV at 290 K). It also raises the question as to whether it is possible to generate entangled photons at these frequencies, as previously this has only been achieved using cryogenically cooled Josephson junctions. A homodyne interferometric receiver is proposed whereby a millimetre wave pump generates entangled photons by spontaneous parametric down-conversion in a non-linear birefringent material, before the signal and idler are mixed together in a sum-frequency mixer. The output then enters a second mixer which uses the pump as the local oscillator to shift the signal and idler down to baseband, where signal integration over many successive entangled pair recovers the entanglement signature from the noise. A successful demonstration of this would mean cryogenics could be avoided, enabling more sensor architectures and deployment scenarios. Novel experiments in the millimetre wave band could lead to a deeper understanding of entanglement and offer novel schemes for secure communications and covert interrogation techniques (quantum radar and ghost imaging), exploiting the fact that the signal is below the level of the thermal noise and can only be accessed by a single user having the key, which is the pump.