Large group of photons on demand – Similar to photonic ‘integrated circuit’

Completely safe, high-speed quantum communication, or even a model of quantum computer, may be among the feasible applications for the novel source of singular photons recently built at the Faculty of Physics at the University of Warsaw Poland. An unexpected feature of this novel equipment is that for the first time it allows the on-demand production of an accurately regulated group of photons, as opposed to just a singular one.

“Compared to current solutions and ideas, our device is much more effective and enables for integration on a bigger scale. In the functional sense, one can even consider it as a first equivalent of a small ‘integrated circuit’ operating on singular photons,” explains Dr. Wojciech Wasilewski, one of the authors of the study.

The primary single-photon sources were introduced in the 1970s, and even though the numerous sorts of them that exist today still have their numerous drawbacks, singular photons can nevertheless be successfully employed in quantum communication protocols that confirm full confidentiality. However, to be able to perform intricate quantum computations we would require entire groups of photons.

photonic 'integrated circuit'

The simplest technique of generating groups of photons is to use a sufficiently large number of sources. The equipment in widespread employ today utilizes the procedure of Spontaneous Parametric Down Conversion – SPDC. Under specific conditions, a photon generated by a laser can split into two novel ones, each with half the volume of energy, and with all other properties linked by the principles of saving energy and momentum. Thus, when we record data on one of the photon from the pair we also find out about the existence and properties of the other photon that nevertheless remains undisturbed by observation and therefore accurately suitable for quantum operations.

Unfortunately, every SPDC source generated singular photons rather quite randomly. As a result, for a simultaneous emission from even as few as 10 sources we might have to wait for up to several years.

In 2013 a group of physicists from the Universities of Oxford and London introduced a much more effective protocol for generating groups of photons. The idea was to place a quantum memory at each source that would be efficient of storing emitted photons. The photons stored in the memories could be released at the same moment.

In the conducted studies the novel source generated a group of up to 60 photons. In addition to quantum computations, the photonic ‘integrated circuit’ may be useful in quantum communication. Presently, this involves sending singular photons employing an optical fiber. The novel source would enable numerous photons to enter the optical fiber simultaneously, and hence would enhance the capacity of quantum channels.