US 12,259,634 B2
Multiplexed single photon source using one-way switching elements
Michele Reilly, Austin, TX (US)
Assigned to Second Foundation, Inc.
Filed by Michele Reilly, Austin, TX (US)
Filed on Mar. 30, 2022, as Appl. No. 17/708,123.
Claims priority of application No. 21166319 (EP), filed on Mar. 31, 2021.
Prior Publication US 2022/0317544 A1, Oct. 6, 2022
Int. Cl. G02F 1/39 (2006.01); H04B 10/70 (2013.01); H04Q 11/00 (2006.01)
CPC G02F 1/39 (2013.01) [H04B 10/70 (2013.01); H04Q 11/0001 (2013.01); H04Q 2011/0018 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A multiplexed single photon source capable of producing pure single photons quasi-deterministically at a predetermined generation time Tg=NTd, with the total number of lap cycles N being a natural number and Td being a delay time, the single photon source comprising:
a pulsed random single photon source capable of randomly producing single photons with a probability p at a production rate corresponding to the inverse of a pump period Tp, wherein, when a single photon is randomly produced during a pulse, it is heralded by a heralding signal and is output on an output mode of the random single photon source;
a first optical switch and a last optical switch, each having a first input mode and a second input mode and a first output mode and a second output mode, wherein:
the first input mode of the first optical switch is connected to the output mode of the random single photon source;
the first output mode of the last optical switch is connected to an output mode of the multiplexed single photon source;
the first and last optical switches moreover each effect a unitary mapping from their respective input modes to their respective output modes, the unitary mapping depending on a state of the respective optical switch, wherein in a first state, the unitary mapping corresponds to a SWAP operation, and in a second state the unitary mapping corresponds to an Identity operation; and
the first and last optical switches are capable of being switched from the first to the second state and/or from the second state to the first state within a switching time Ts, the switching time Ts being smaller than or equal to the delay time Td, by a control signal;
a closed optical path comprising a delay loop introducing a time delay equal to the delay time Td to a photon and connecting the second output mode of the last optical switch to second input mode of the first optical switch; and
a control unit controlling each of the first and last optical switches based on the heralding signal and the cycle number N, the cycle number corresponding to a maximum number of times a photon may loop around the closed optical path before being output,
wherein, before or at the start of a first lap cycle, the control unit is configured to initialize the first optical switch in the first state and, if applicable, the last optical switch in the second state, such that, upon generation of a first photon by the random single photon source, that photon enters the first input mode of the first optical switch and, by being output on the second output mode of the first optical switch, is routed onto the closed optical path,
wherein, based upon the heralding signal heralding the first photon, the control unit is configured to switch the first optical switch from its first state to its second state after the photon has been routed onto the closed optical path, thereby ensuring that the first photon loops around the closed optical path as long as the first and last optical switches remain in their respective second states,
and, wherein, in an Nth lap cycle, the control unit is configured to switch the last optical switch from the second state to the first state, thereby causing the first photon on the closed optical path to be routed to the first output mode of the last optical switch and thus being output on the output mode of the multiplexed single photon source.