Abstract: The various embodiments described herein include methods, devices, and systems for operating superconducting circuits. In one aspect, an electric circuit includes: (1) a superconductor component having a first terminal at a first end and a second terminal at a second end; (2) a gate component thermally-coupled to the superconductor component at a first location between the first terminal and the second terminal, where the gate component is thermally-coupled via a first section of the gate component; and where the gate component has a smallest width at the first section so as to focus resistive heating toward the superconductor component.

Abstract: A quantum device includes a cryogenic chamber and a quantum computing module positioned within the cryogenic chamber. The quantum computing module includes a silicon substrate and a quantum circuit (QC) die including a qubit integrated circuit. The QC die is attached to the silicon substrate. An electronic circuit (EC) die including an electronic integrated circuit is attached to the QC die such that the qubit integrated circuit and the electronic integrated circuit face each other. The QC die can be fusion bonded to the EC die. A circuit board (CB) includes a power converter configured to convert input power received from a cryogenic chamber feedthrough to output power that is coupled to the QC die and to the EC die.

Abstract: An electronic device includes a substrate and a layer of superconducting material disposed over the substrate. The layer of superconducting material includes a first wire and a loop that is (1) distinct and separate from the first wire and (ii) capacitively coupled to the first wire while the loop and the first wire are in a superconducting state.

Abstract: A waveguide structure includes a substrate and a waveguide core coupled to the substrate and including a first material characterized by a first index of refraction and a first electro-optic coefficient. The waveguide structure also includes a first cladding layer at least partially surrounding the waveguide core and including a second material characterized by a second index of refraction less than the first index of refraction and a second electro-optic coefficient greater than the first electro-optic coefficient. The second cladding layer is coupled to the first cladding layer.

Abstract: A frequency conversion system includes a bus waveguide, a first pump laser coupled to the bus waveguide and characterized by a first frequency, a second pump laser coupled to the bus waveguide and characterized by a second frequency, an input light combining device coupled to the bus waveguide and configured to combine light from the first pump laser and the second pump laser to produce a combined light, and a plurality of optical resonators coupled to the bus waveguide. Each optical resonator of the plurality of optical resonators has a respective resonance line width, wherein for each optical resonators of the plurality the respective resonance line width overlaps with a resonance line width of at least one adjacent optical resonator of the plurality of optical resonators, and wherein each optical resonator of the plurality is configured to generate output light at a converted frequency via frequency mixing.

Abstract: Photonic devices are disclosed including a first cladding layer, a first electrical contact comprising a first lead coupled to a first dielectric portion, a second electrical contact comprising a second lead coupled to a second dielectric portion, a waveguide structure comprising a slab layer comprising a first material, and a second cladding layer. The slab layer may be coupled to the first dielectric portion of the first electrical contact and the second dielectric portion of the second electrical contact. The first dielectric portion and the second dielectric portion may have a dielectric constant greater than a dielectric constant of the first material.

Abstract: A method of generating an m-photon entangled state includes inputting photons into a plurality of sets of modes. Each set of modes is coupled to a different set of modes. The method includes detecting photons in the plurality of sets of modes. The method includes, in accordance with a determination, based on a number of photons detected, that more than m-photons remain in the plurality of sets of modes: performing a second detection operation that includes detecting photons in the plurality of sets of modes; determining, based at least in part on a number of photons detected, whether the photons remaining in the plurality of sets of modes after the second detection operation are in the m-photon entangled state; and in accordance with a determination that the photons remaining in the plurality of sets of modes are in the m-photon entangled state, outputting the remaining photons.

Abstract: A method includes obtaining a plurality of entangled qubits, with high fault tolerance, represented by a lattice structure. The lattice structure includes a plurality of contiguous lattice cells. A first subset of the plurality of entangled qubits defines a first plane, and a second subset of the plurality of entangled qubits defines a second plane that is parallel to and offset from the first plane. The plurality of entangled qubits includes a defect qubit that is entangled with at least one face qubit on the first plane and at least one edge qubit on the second plane.

Abstract: The various embodiments described herein include methods, devices, and systems for operating superconducting circuitry. In one aspect, a programmable circuit includes: (1) a superconducting component arranged in a multi-dimensional array of alternating narrow and wide portions, the superconducting component having an input terminal at a first end and an output terminal at a second end opposite of the first end; and (2) control circuitry coupled to the narrow portions of the superconducting component, the control circuitry configured to transition the narrow portions between superconducting and non-superconducting states. In some implementations, the superconducting component and the control circuitry are formed on different layers of the programmable circuit.

Abstract: A wafer includes a silicon layer, a first dielectric layer on the silicon layer, and a ferroelectric layer on the first dielectric layer. The ferroelectric layer defines one or more gaps between portions of the ferroelectric layer. The wafer also includes a second dielectric layer on the ferroelectric layer and disposed within the one or more gaps.

Abstract: An electro-optic device includes a substrate and a waveguide on the substrate. The waveguide includes a layer stack including a plurality of electro-optic material layers interleaved with a plurality of interlayers and a waveguide core adjacent to the layer stack. The waveguide may include a pair of electrodes in electrical contact with the plurality of electro-optic material layers. The plurality of interlayers maintains a first lattice structure at room temperature and a cryogenic temperature. The plurality of electro-optic material layers maintains a second lattice structure and crystallographic phase at the room temperature and the cryogenic temperature.

Abstract: A device includes a die stack including a first die including a quantum circuit and a second die including an electronic circuit. The second die and the first die face each other. The device also includes a first interconnect between the quantum circuit and the electronic circuit and a second interconnect between the quantum circuit and the electronic circuit.

Abstract: A Mach-Zehnder interferometer (MZI) filter comprising one or more passive compensation structures are described. The passive compensation structures yield MZI filters that are intrinsically tolerant to perturbations in waveguide dimensions and/or other ambient conditions. The use of n+1 waveguide widths can mitigate n different sources of perturbation to the filter. The use of at least three different waveguide widths for each Mach-Zehnder waveguide can alleviate sensitivity of filter performance to random width or temperature variations. A tolerance compensation portion is positioned between a first coupler section and a second coupler section, wherein the tolerance compensation portion includes a first compensation section having a second width, a second compensation section having a third width and a third compensation section having a fourth width, wherein the fourth width is greater than the third width and the third width is greater than the second width.

Abstract: Techniques disclosed herein relate to photon sources with high spectral purity and high brightness. In one embodiment, a photon-pair source includes a pump waveguide, a first resonator coupled to the pump waveguide to couple pump photons from the pump waveguide into the first resonator, a second resonator coupled to the first resonator, and an output waveguide coupled to the second resonator. The second resonator is configured to convert the pump photons into photon pairs. The second resonator and the first resonator are configured to cause a coupling-induced resonance splitting in the second resonator or the first resonator. The second resonator and the output waveguide are configured to couple the photon pairs from the second resonator into the output waveguide. In some embodiments, the photo-pair source includes one or more tuners for tuning at least one of the first resonator or the second resonator.

Abstract: A system for generating clock signals for a photonic quantum computing system includes a pump photon source configured to generate a plurality of pump photon pulses at a first repetition rate, a waveguide optically coupled to the pump photon source, and a photon-pair source optically coupled to the first waveguide. The system also includes a photodetector optically coupled to the photon-pair source and configured to generate a plurality of electrical pulses in response to detection of at least a portion of the plurality of pump photon pulses at the first repetition rate and a clock generator coupled to the photodetector and configured to convert the plurality of electrical pulses into a plurality of clock signals at the first repetition rate.

Abstract: A photonic switch includes a first waveguide including a first region extending between a first coupler section and a second coupler section and a second region extending between the second coupler section and a third coupler section. The photonic switch also includes a second waveguide including a first portion extending between the first coupler section and the second coupler section, the first portion including at least two first compensation sections each having a different waveguide width, and a second portion extending between the second coupler section and the third coupler section, the second portion including at least two second compensation sections each having a different waveguide width. The photonic switch further includes at least one variable phase-shifter disposed in at least one of the first waveguide or the second waveguide.

Abstract: A method and a device for correcting quantum state information are disclosed. A decoder receives information identifying syndrome values for a plurality of entangled qubit states represented by a graph state with a respective edge of the graph state corresponding to a respective qubit state of the plurality of entangled qubit states. The decoder repeats identifying one or more clusters of qubit states and/or syndrome states in the graph state until all of the one or more identified clusters are determined to be valid while increasing a size of a respective cluster each time the identifying operation is performed. The decoder reconstructs one or more qubit states and/or syndrome states for respective clusters; and stores information identifying the one or more reconstructed qubit states and/or syndrome states.

Abstract: Circuits and methods that implement multiplexing for photons propagating in waveguides are disclosed, in which an input photon received on a selected one of a set of input waveguides can be selectably routed to one of a set of output waveguides. The output waveguide can be selected on a rotating or cyclic basis, in a fixed order, and the input waveguide can be selected based at least in part on which one(s) of a set of input waveguides is (are) currently propagating a photon.

Abstract: An optical switch structure includes at least one optical input port and at least one optical output port. The optical switch structure also includes an optical waveguide structure including a waveguide core and a waveguide cladding The optical waveguide structure is optically coupled to the at least one optical input port and the at least one optical output port. The waveguide core includes a first material characterized by a first index of refraction and a first electro-optic coefficient and the waveguide cladding includes a second material characterized by a second index of refraction less than the first index of refraction and a second electro-optic coefficient greater than the first electro-optic coefficient.

Abstract: A photon source includes a bus waveguide, a photon source pump laser coupled to the bus waveguide and a plurality of optical resonators coupled to the bus waveguide. Each optical resonator of the plurality of optical resonators has a respective resonance line width and a respective resonance frequency, wherein a bandwidth of the resonant center frequencies of the plurality of optical resonators is greater than a bandwidth of the photon source pump laser. The bus waveguide produces photons in response to receiving laser pulses from the pump laser.