In the fields of quantum information, quantum optics, quantum cryptography, and quantum communications, there is a need to generate entangled photon pairs. The entangled photon pairs are described by an inseparable wave equation such that if a measurement is performed on one photon, its twin’s photon state is completely determined. The problem up to now is that these sources of entangled photons require large, expensive, and power-intensive Ar-ion lasers to generate light in the UV to pump a nonlinear crystal to produce spontaneous parametric down conversion (SPDC). The SPDC process generates a pair of photons (the signal and the idler) whose momentum and energy sum up to equal the initial pump photon.
Current systems are bulky, slow, and power-hungry. These units are constructed from large optical parts, adding bulk and cost. Despite the large amount of power required, the photons are low-energy.
This innovation, a compact source of polarization-entangled photons, includes a laser source producing a laser beam, a pair of nonlinear crystals in optical contact with each other with one of the pair of nonlinear crystals having an input face and the laser beam incident on the input face, and another of the path of nonlinear crystals rotated 90° along an axis perpendicular to the input face, with respect to each other, and a fiber coupling point, configured to receive a pair of singlemode fibers. Pairs of polarization-entangled photons are produced through spontaneous parametric down conversion of the laser beam and provided to the fiber coupling point.
The device is able to provide 80,000 to 8,000,000 polarization-entangled photon pairs per second in the 800-nm range while requiring only milliwatts of electrical power. This represents an efficiency increase of about a million times greater than conventional techniques. This device can be optically coupled (pigtailed) for convenience. The unit is ruggedized for harsh environments. Using solid-state and monolithic construction brings its cost down due to cost-effective batch-manufacturing techniques.