News Column

Researchers Submit Patent Application, "Chip Integrated Single Photon Generation by Active Time Multiplexing", for Approval

June 26, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Mower, Jacob (New York, NY); Englund, Dirk R. (New York, NY), filed on January 7, 2014, was made available online on June 12, 2014.

The patent's assignee is The Trustees of Columbia University in the City of New York.

News editors obtained the following quote from the background information supplied by the inventors: "The disclosed subject matter relates generally to techniques for converting signal and idler photons generated by a nonlinear optics into a deterministic stream of single photons.

"Single-photon sources are utilized in a number applications, including quantum information science, quantum computing/simulation, quantum cryptography/quantum key distribution, quantum teleportation, precision measurements and sensing, tests of quantum nonlocality, and high resolution lithography. For example, complex nonclassical optical states required for quantum metrology can be constructed from single-photon sources. Additionally, nondeterministic logic operations between multiple photonic qubits, combined with the ability to detect when gates have succeeded (feed-forwardability), can allow for efficient quantum computation.

"To realize these and other quantum information technologies, efficient sources of indistinguishable single photons are useful. Certain techniques for generation of indistinguishable single photons include the application of quantum dots in micro- and nano-cavities, isolated cold atoms, and isolated single molecules in solid-state systems. However, they can require complex setups, including high vacuum and cryogenic temperatures, not immediately suitable for scalability.

"While spontaneous parametric down conversion can produce highly indistinguishable single photons, generation is nondeterministic. Techniques for the generation of on-demand single photons using spontaneous parametric down conversion can be large and expensive, employing bulk optics. Moreover, such techniques can employ photon capture schemes that suffer from high loss, particularly when scaled up.

"Accordingly, there is a need for an improved technique to provide sources of indistinguishable, on-demand single photons."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In one aspect of the disclosed subject matter, a system including a photonic integrated circuit for converting signal and idler photons generated by nonlinear optics into a deterministic stream of single photons is provided. An exemplary system includes an optical element for receiving a heralded, nondeterministic source of signal and idler photons from the nonlinear optics. The system can include a separating element, adapted to intercept the emission path from the optical element, for separating one or more signal photons from one or more temporally corresponding idler photons.

"In certain embodiments, the system can include a variable delay circuit which is optically coupled to the separating element, adapted to receive the one or more signal photons, and configured to delay the emission of at least one of the one or more signal photons using a variable optical buffer. It can also include a heralding decision control to receive the one or more idler photons and determine whether at least one of the one or more signal photons should enter the variable delay circuit, and if so, a delay length of the variable optical buffer.

"In one embodiment, the nonlinear optics can include a type-II spontaneous parametric down conversion element to generate signal and idler photons. The spontaneous down conversion element can include a pump light source that generates pump light, a set of beam splitters and delay arms for splitting the pump light into a series of delays, thus generating a pulse train, and a non-linear crystal arranged to receive the pulse train and generate the signal and idler photons. In one embodiment, the non-linear crystal can be implemented on the photonic integrated chip. Alternatively, the nonlinear optics can include a four-wave mixing element to generate signal and idler photons. The four-wave mixing element can be implemented onto the photonic integrated chip.

"In one embodiment, the variable optical buffer can include at least one optical delay line. For example, the variable buffer can include a plurality of static delays of predetermined lengths and a plurality of 2.times.2 switches, each switch coupled to a static display and in communication with the heralding decision control. The plurality of switches can be modulated by the heralding decision control. Alternatively, the variable optical buffer can include an optical resonator.

"In one embodiment, the heralding decision control can be configured to detect a time of arrival associated with the at least one idler photon and the plurality of switches can be modulated according to the time of arrival. The heralding decision control can include at least one single photon detector for detecting the at least one idler photon, a data processor to receive a bit stream corresponding to a detection event from the single photon detector, and a bit generator to receive a processed bit stream from the processor and modulate a decision switch, thereby selecting whether the signal photon will enter the variable delay circuit.

"In one embodiment, the system can include a clock set to a predetermined period and coupled to an element of the nonlinear process, the heralding decision control, and the variable control circuit. The predetermined lengths of the variable delay circuit can be multiples of the predetermined period.

"In one embodiment, the heralding decision control can repeatedly detect a plurality of times of detection associated with a plurality of idler photons. The plurality of switches can be modulated according to the time of arrival, thereby emitting a plurality of single photons at a multiple of the predetermined period. That is, the heralding decision control can be configured to emit a deterministic, periodic stream of single photons. Alternatively, the heralding decision control can be configured to emit a non-periodic stream of single photons.

"In another aspect of the disclosed subject matter, a method for converting signal and idler photons generated by a nonlinear optical process into a deterministic stream of single photons is provided. One example method includes receiving a heralded, nondeterministic source of signal and idler photons from the nonlinear optical process. One or more signal photons are separated from one or more temporally corresponding idler photons received by the optical element with a separating element placed in an emission path from the optical element. A determination is made as to whether at least one of the signal photons should be variably delayed, and if so, the delay length is determined. A variable delay circuit receives the one or more signal photons from the separating element, and delays, by the determined delay length, if any, the emission of at least one of the one or more signal photons with a variable optical buffer.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a schematic diagram of a system for converting signal and idler photons generated by a nonlinear optical system into a deterministic stream of single photons in accordance with an embodiment of the disclosed subject matter.

"FIG. 2 is a flow diagram of a method for converting signal and idler photons generated by a nonlinear optical system into a deterministic stream of single photons in accordance with an embodiment of the disclosed subject matter.

"FIG. 3 is a depiction of a photonic integrated chip for converting signal and idler photons generated by a nonlinear optical system into a deterministic stream of single photons in accordance with an embodiment of the disclosed subject matter.

"FIG. 4 is a representation of actively multiplexed parametric photon generation according an embodiment of the disclosed subject matter.

"Throughout the drawings, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the disclosed subject matter will now be described in detail with reference to the Figs., it is done so in connection with the illustrative embodiments."

For additional information on this patent application, see: Mower, Jacob; Englund, Dirk R. Chip Integrated Single Photon Generation by Active Time Multiplexing. Filed January 7, 2014 and posted June 12, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3546&p=71&f=G&l=50&d=PG01&S1=20140605.PD.&OS=PD/20140605&RS=PD/20140605

Keywords for this news article include: The Trustees of Columbia University in the City of New York.

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Source: Politics & Government Week


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