Integrated superconducting nanowire digital photon detector
Superconducting nanowire single photon detectors have recently been developed for a wide range of applications, including imaging and communications. An improved detection system is disclosed, whereby the detectors are monolithically integrated on the same chip with Josephson junctions for control and data processing. This enables an enhanced data rate, thereby facilitating several new and improved applications. A preferred embodiment comprises integrated digital processing based on single-flux-quantum pulses. An integrated multilayer fabrication method for manufacturing these integrated detectors is also disclosed. Preferred examples of systems comprising such integrated nanowire photon detectors include a time-correlated single photon counter, a quantum random number generator, an integrated single-photon imaging array, a sensitive digital communication receiver, and quantum-key distribution for a quantum communication system.
1 . A photon detector, comprising:
a superconducting nanowire;
a Josephson junction in series with the nanowire;
a bias generator, configured to bias the superconducting nanowire in series with the Josephson junction, such that absent a photon absorbed by the superconducting nanowire the Josephson junction has a bias voltage, and when the photon is absorbed by the superconducting nanowire, the superconducting nanowire generates a voltage pulse,
the superconducting nanowire and the Josephson junction being integrated on a common substrate.
2 . The photon detector according to claim 1 , wherein absorption of the photon causes a decrease in a critical current of at least a portion of the superconducting nanowire, wherein the bias induces a current above the decreased critical current and the voltage pulse.
3 . The photon detector according to claim 1 , wherein a kinetic inductance of the superconducting nanowire is 1 nH or less, and the superconducting nanowire is configured to recover from absorption of the photon sufficiently fast to produce voltage pulses at a rate of at least 1 GHz and having a pulsewidth of less than 0.1 ns, wherein.
4 . The photon detector according to claim 1 , further comprising a circuit configured to control the bias generator to maintain the bias at a level which suppresses spontaneous voltage pulses from the superconducting nanowire.
5 . The photon detector of claim 1 , further comprising a pulse discriminator circuit configured to convert the voltage pulse to a single-flux-quantum (SFQ) pulse.
6 . The photon detector of claim 1 , further comprising an digital counter and a time-to-digital converter, wherein the digital counter is configured to count the pulse from the voltage pulse and the time-to-digital converter is configured to determine a pulse latency of the voltage pulse.
7 . The photon detector of claim 1 , further comprising a circuit configured to tune a critical current of the Josephson junction.
8 . The photon detector of claim 1 , further comprising a conductive loop, wherein the Josephson junction and the loop are configured as a SQUID.
9 . The photon detector of claim 8 , wherein the SQUID has a loop current, further comprising a multi-flux-quantum (MFQ) memory cell, wherein a circulating supercurrent in the multi-flux-quantum (MFQ) memory cell is adapted to digitally tune the SQUID by altering the loop current.
10 . The photon detector of claim 1 , further comprising a shunt resistor in parallel with the superconducting nanowire, having resistance less than a resistance of the superconducting nanowire during the voltage pulse.
11 . A photon detector, comprising:
a superconducting quantum interference device, comprising two Josephson junctions within a superconducting inductive loop;
a superconducting nanowire, configured to absorb a photon to cause a temporary and localized decrease in a critical current of the superconducting nanowire, the superconducting nanowire and the superconducting quantum interference device being integrated and configured to operate within a common environment; and
a bias circuit configured to generate a voltage bias across the superconducting nanowire and the superconducting quantum interference device, through the two Josephson junctions in parallel, wherein the critical current of the superconducting nanowire is above a critical current of the two Josephson junctions.
12 . The photon detector according to claim 11 , further comprising a single flux quantum logic circuit configured to detect a voltage pulse in the superconducting nanowire due to the temporary and localized decrease in the critical current of the superconducting nanowire.
13 . The photon detector according to claim 12 , wherein the single flux quantum logic circuit is further configured to count a number of voltage pulses in the superconducting nanowire.
14 . The photon detector according to claim 12 , wherein the single flux quantum logic circuit is further configured to determine a timing of voltage pulses in the superconducting nanowire.
15 . The photon detector according to claim 11 , further comprising a control circuit magnetically coupled to the superconducting inductive loop, configured to tune the critical current of the two Josephson junctions.
16 . The photon detector according to claim 15 , wherein the control circuit is configured to add and remove single flux quanta to and from the superconducting inductive loop, to thereby alter a current circulating in the superconducting inductive loop.
17 . The photon detector according to claim 16 , wherein the bias circuit is configured to establish the bias current at about 90% of the critical current of the superconducting nanowire, and the control circuit is configured to add and remove single flux quanta to and from the superconducting inductive loop to optimize a response of the superconducting nanowire to the photon.
18 . The photon detector according to claim 11 , wherein the photon detector is configured to operate at an operating cryogenic temperature, further comprising a resistive shunt that remains resistive at the operating cryogenic temperature, to carry current and to couple magnetic flux into the superconducting loop to decrease the critical current of the two Josephson junctions during the voltage spike.
19 . The photon detector according to claim 11 , wherein the bias circuit comprises a rapid flux single quantum logic circuit.
20 . A method of detecting a photon, comprising:
providing a superconducting quantum interference device, comprising two Josephson junctions within a superconducting inductive loop, and a superconducting nanowire, configured to absorb a photon to cause a temporary and localized decrease in a critical current of the superconducting nanowire, the superconducting nanowire and the superconducting quantum interference device being integrated and configured to operate within a common environment;
generating a voltage bias across the superconducting nanowire and the superconducting quantum interference device with a bias circuit, the bias voltage causing a current through the superconducting nanowire and the two Josephson junctions in parallel, wherein the critical current of the superconducting nanowire is above a critical current of the two Josephson junctions;
exposing the superconducting nanowire to the photon, absorbing the photon by the superconducting nanowire, causing the critical current in the superconducting nanowire to drop below the current from the bias voltage, and generating a voltage pulse across the superconducting nanowire.