Apparatus and methods for quantum key distribution
Systems, apparatus, and methods using an integrated photonic chip capable of operating at rates higher than a Gigahertz for quantum key distribution are disclosed. The system includes two identical transmitter chips and one receiver chip. The transmitter chips encode photonic qubits by modulating phase-randomized attenuated laser light within two early or late time-bins. Each transmitter chip can produce a single-photon pulse either in one of the two time-bins or as a superposition of the two time-bins with or without any phase difference. The pulse modulation is achieved using ring resonators, and the phase difference between the two time-bins is obtained using thermo-optic phase shifters and/or time delay elements. The receiver chip employs either homodyne detection or heterodyne detection to perform Bell measurements.
1. An apparatus for distributing a quantum key, the apparatus comprising:
an input waveguide;
a first ring resonator, evanescently coupled to the input waveguide, to receive a first pulse of light via the input waveguide;
a second ring resonator, evanescently coupled to the input waveguide, to receive a second pulse of light via the input waveguide;
an output waveguide, evanescently coupled to the first ring resonator and the second ring resonator, to receive the first pulse of light from the first ring resonator and the second pulse of light from the second ring resonator; and
at least one modulator, operably coupled to at least one of the first ring resonator, the second ring resonator, and the output waveguide, to delay at least one of the first pulse of light or the second pulse of light so as to generate a photonic qubit in an X-basis or a Z-basis,
wherein the first ring resonator is configured to emit a third pulse of light and the at least one modulator is configured to delay the third pulse of light with respect to the first pulse of light so as to form a |+ state in the X-basis.
2. The apparatus of claim 1 , wherein the at least one modulator is configured to delay third pulse of light with respect to the first pulse of light by a period equal to an integer multiple of an oscillation period of a carrier of the first pulse of light.
3. The apparatus of claim 1 , wherein the at least one modulator is configured to delay the first pulse of light with respect to the second pulse of light so as to form the photonic qubit in a |− state in the X-basis.
4. The apparatus of claim 1 , wherein the at least one modulator is configured to delay the first pulse of light with respect to the second pulse of light by a period selected to create a π phase difference between the first pulse of light and the second pulse of light.
5. The apparatus of claim 1 , wherein the at least one modulator is configured to delay the first pulse so as to form the photonic qubit in a state in the Z-basis.
6. The apparatus of claim 1 , wherein the at least one modulator comprises a phase shifter, operably coupled to the output waveguide, to vary a phase difference between the first pulse of light and the second pulse of light.
7. The apparatus of claim 1 , wherein the output waveguide comprises:
a receiving section;
a propagation section to guide the first light received by the receiving section; and
a loop section having at least one segment evanescently coupled to the propagation section so as to couple at least a portion of the first pulse of light back to the propagation section,
wherein at least one of the first ring resonator and the second ring resonator is evanescently coupled to the propagation section of the input waveguide.
8. The apparatus of claim 1 , further comprising:
a detector, optically coupled to the input waveguide, to monitor an intensity of the first pulse of light.
9. The apparatus of claim 1 , further comprising:
a phase randomized light source, in optical communication with the input waveguide, to provide the first pulse of light and the second pulse of light.
10. The apparatus of claim 1 , further comprising:
an attenuator, operably coupled to the output waveguide, to attenuate an intensity of at least one of the first pulse of light and the second pulse of light so as to create a decoy state.
11. The apparatus of claim 1 , further comprising:
a phase shifter, operably coupled to the output waveguide between the first ring resonator module and the second resonator module, to apply a phase shift to the second pulse of light.
12. An apparatus for distributing a quantum key, the apparatus comprising:
an input waveguide;
a first ring resonator, evanescently coupled to the input waveguide, to receive a first pulse of light via the input waveguide;
a second ring resonator, evanescently coupled to the input waveguide, to receive a second pulse of light via the input waveguide;
an output waveguide, evanescently coupled to the first ring resonator and the second ring resonator, to receive the first pulse of light from the first ring resonator and the second pulse of light from the second ring resonator;
at least one modulator, operably coupled to at least one of the first ring resonator, the second ring resonator, and the output waveguide, to delay at least one of the first pulse of light or the second pulse of light so as to generate a photonic qubit in an X-basis or a Z-basis; and
a photonic integrated receiver to detect the photonic qubit, wherein the photonic integrated receiver comprises:
a substrate;
a coupler fabricated in the substrate and comprising:
a first input waveguide to receive qubits provided by a first party;
a second input waveguide to receive qubits provided by a second party;
a first output waveguide; and
a second output waveguide;
a first detector coupled to the first output waveguide; and
a second detector coupled to the second output waveguide.
13. A method of distributing a quantum key using a transmitter comprising an input waveguide, a first ring resonator evanescently coupled to the input waveguide, a second ring resonator evanescently coupled to the input waveguide, and an output waveguide evanescently coupled to the first ring resonator and the second ring resonator, the method comprising:
selecting one of an X-basis and a Z-basis for distributing the quantum key;
in response to selection of the Z-basis, performing at least one of:
delaying a first pulse of light propagating in the first ring resonator to create the quantum key in a |0 state in the Z-basis; and
delaying the first pulse of light propagating in the first ring resonator to create the quantum key in a |1 state in the Z-basis; and
in response to selection of the X-basis, performing at least one of:
delaying the first pulse of light propagating in the first ring resonator with respect to a second pulse of light propagating in at least one of the first ring resonator or the second ring resonator to constructively interfere the first pulse of light with the second pulse of light so as to create the quantum key in an |+ state in the Z-basis; and
delaying the first pulse of light propagating in the first ring resonator with respect to the second pulse of light propagating in at least one of the first ring resonator or the second ring resonator to destructively interfere the first pulse of light with the second pulse of light so as to create the quantum key in an |− state in the Z-basis.
14. The method of claim 13 , wherein selecting one of the Z-basis and the X-basis comprises randomly selecting one of the Z-basis and the X-basis.
15. The method of claim 13 , wherein modulating the first ring resonator comprises at least one of thermally modulating or electro-optically modulating the first ring resonator.
16. The method of claim 13 , further comprising:
propagating the first pulse of light in a propagation section of the output waveguide;
propagating the first pulse of light through at least one of the first ring resonator and the second ring resonator evanescently coupled to the propagation section of the output waveguide; and
coupling at least a portion of the first pulse of light back to the propagation section of the output waveguide.
17. The method of claim 13 , wherein delaying the first pulse of light propagating in the first ring resonator comprises delaying a phase randomized attenuated laser pulse propagating in the first ring resonator.
18. The method of claim 13 , further comprising:
attenuating the quantum key to create a decoy state.
19. The method of claim 13 , wherein delaying the first pulse of light propagating in the first ring resonator with respect to a second pulse of light propagating in the second ring resonator comprises applying a π-phase shift to the second pulse of light with respect to the first pulse of light.
20. An apparatus for measurement-device-independent quantum key distribution, the apparatus comprising:
an input waveguide to guide an input pulse of light;
an output waveguide comprising:
a receiving section, evanescently coupled to the input waveguide, to receive the input pulse of light;
a propagation section to guide the input pulse of light received by the input section; and
a loop section having at least one segment evanescently coupled to the propagation section so as to couple at least a portion of the input pulse of light back to the propagation section; and
a first ring resonator evanescently coupled to the propagation section of the output waveguide;
a first modulator, operably coupled to the first ring resonator, to delay a first pulse of light propagating in the first ring resonator;
a second ring resonator evanescently coupled to the propagation section of the output waveguide; and
a second modulator operably coupled to the second ring resonator and having a first modulation mode and a second modulation mode,
wherein, in the first modulation mode, the second modulator delays a second pulse of light propagating in the second ring resonator so as to cause the first pulse of light to constructively interfere with the second pulse of light and, in the second modulation mode, the second modulator delays the second pulse of light so as to cause the first pulse of light to destructively interfere with the second pulse of light.