–

Here is the introduction to the patent which has a UK grant, referred to in the dream…

–

Increasing the probability of generating entangled photon pairs using Electric Field Induced Spontaneous Parametric Down Conversion

Field of the invention.

The present invention relates to optical sources of entangled pairs of photons whereby said entangled photons are in quantum superposition states, these sources are either stand alone, are fibre coupled or are in photonic circuits including optical waveguides.  The invention provides for an enhanced method of production of said photon pairs and the control thereof by the application of a time varying direct current electric field applied to the medium in which photon pair production takes place. The invention is an Electric Field Induced Spontaneous Parametric Down Conversion (EFISPDC) source of correlated photon pairs capable of high repetition rates which increases both the flexibility and potential uses of said source by the addition of an externally controllable parameter, namely the amplitude, direction and waveform of an applied electric field. 

Background

In recent times the field of quantum optics has burgeoned and there is a vast amount of research worldwide on this subject. There is much interest in so-called quantum cryptography, quantum teleportation, quantum information processing, heralded photons and the long-term prospect of commercially viable quantum computing. Just as is the case with any emergent new technology there will be a technology life cycle. The machines of tomorrow will not be those of today. There has been and currently is, a great deal of activity in the realms of intellectual property pertaining to these fields. The research in this area will generate new ideas and unanticipated applications thereof. Governments are interested in such new technologies because they may offer strategic advantages both in terms of economy and defence. Large corporations are investing with a long-term view and in the fullness of time commercially viable products will arise. What they are or maybe, remains to be seen.

As such this new endeavour will need Key Enabling Technology (KET) the current invention is one such technology. Much of the endeavour in entangled photon pairs research is based upon Spontaneous Parametric Down Conversion (SPDC) (for example patent reference Kwiat et al. US 6424665 B1) though there is also research into bi-exciton states inter alia. The current scientific explanation of SPDC is something of a hybrid in that it uses classical non-linear optics to explain the power and phase-matching conditions required yet it invokes a quantum mechanical treatment of the electric field to account for its occurrence. This is because SPDC is a classically forbidden process in the absence of significant pump beam depletion. It is only when a quantization of the field is invoked that the process can be explained via photon creation and annihilation operators. It should be stressed that this process on its own is probabilistic and cannot be directly controlled.

In SPDC a laser is input into a non-linear optical medium, and from time to time, one of the input photons is annihilated to produce two lower energy daughter photons. The sum of the energy of these two daughter photons is equal to the energy of the parent photon within the limit of the quantum mechanical uncertainty principle. The parameters available to those skilled in the art are input laser power, laser frequency, laser bandwidth, laser temporal shape and polarisation, choice of non-linear material and the phase matching of the input laser beam photons with the output beam photons. The properties of the non-linear material may be changed by adjusting the temperature or by crystal cleavage and aligning its crystallographic orientation with respect to the input and output photons, further the non-linear material may be periodically poled. But when SPDC occurs it is a spontaneous, statistical or random process.  SPDC occurs in three variants denominated type 0, type 1(I) and type 2(II) according to the phase matching conditions which prevail.

Method of producing entangled photon pairs using electric field induced spontaneous parametric down conversion.

One can think of SPDC as being closely related to the phenomenon of optical Second Harmonic Generation (SHG) where two photons of equal energy add together by annihilation to create a third photon of higher energy equal to the sum of the energies of the annihilated photons.

.