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: A method includes receiving a plurality of quantum systems, wherein each quantum system of the plurality of quantum system includes a plurality of quantum sub-systems in an entangled state, and wherein respective quantum systems of the plurality of quantum systems are independent quantum systems that are not entangled with one another. The method further includes performing a plurality of joint measurements on different quantum sub-systems from respective ones of the plurality of quantum systems, wherein the joint measurements generate joint measurement outcome data and determining, by a decoder, a plurality of syndrome graph values based on the joint measurement outcome data.

Abstract: An electronic device (e.g., a diode) is provided that includes a substrate and a patterned layer of superconducting material disposed over the substrate. The patterned layer forms a first electrode, a second electrode, and a loop coupling the first electrode with the second electrode by a first channel and a second channel. The first channel and the second channel have different minimum widths. For a range of current magnitudes, when a magnetic field is applied to the patterned layer of superconducting material, the conductance from the first electrode to the second electrode is greater than the conductance from the second electrode to the first electrode.

Abstract: An apparatus includes a plurality of first optical devices and a second optical device. Each first optical device includes a respective first pair of waveguides comprising a respective first waveguide and a respective second waveguide that are coupled together, a respective second pair of waveguides comprising a respective third waveguide and a respective fourth waveguide that are coupled together, and a first fusion gate that includes a detector. Each first fusion gate is configured to perform a fusion on the respective second waveguide and the respective third waveguide of a respective first optical device. The fusion produces a detection pattern for the respective first optical device. The apparatus further includes a multiplexer to select a respective first optical device of the plurality of first optical devices based at least in part on the detection pattern for the respective first optical device and output photons from the respective first optical device.

Abstract: Techniques disclosed herein relate generally to photonic integrated circuits working at cryogenic temperatures. In one example, a device includes a substrate, a dielectric layer on the substrate, an optical waveguide in the dielectric layer, a superconducting circuit in the dielectric layer and coupled to the optical waveguide, and a micro-channel in the dielectric layer and adjacent to the superconducting circuit. The micro-channel is aligned with the superconducting circuit and is configured to conduct a liquid at a cryogenic temperature to locally cool the superconducting circuit.

Abstract: Techniques disclosed herein relate to devices that each include one or more photonic integrated circuits and/or one or more electronic integrated circuits. In one embodiment, a device includes a silicon substrate, a die stack bonded (e.g., fusion-bonded) on the silicon substrate, and a printed circuit board (PCB) bonded on the silicon substrate, where the PCB is electrically coupled to the die stack. The die stack includes a photonic integrated circuit (PIC) that includes a photonic integrated circuit, and an electronic integrated circuit (EIC) die that includes an electronic integrated circuit, where the EIC die and the PIC die are bonded face-to-face (e.g., by fusion bonding or hybrid bonding) such that the photonic integrated circuit and the electronic integrated circuit face each other. In some embodiments, the device also includes a plurality of optical fibers coupled to the photonic integrated circuit.

Abstract: Techniques disclosed herein relate to devices that each include one or more photonic integrated circuits and/or one or more electronic integrated circuits. In one embodiment, a device includes a silicon substrate, a die stack bonded (e.g., fusion-bonded) on the silicon substrate, and a printed circuit board (PCB) bonded on the silicon substrate, where the PCB is electrically coupled to the die stack. The die stack includes a photonic integrated circuit (PIC) that includes a photonic integrated circuit, and an electronic integrated circuit (EIC) die that includes an electronic integrated circuit, where the EIC die and the PIC die are bonded face-to-face (e.g., by fusion bonding or hybrid bonding) such that the photonic integrated circuit and the electronic integrated circuit face each other. In some embodiments, the device also includes a plurality of optical fibers coupled to the photonic integrated circuit.

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 (i) 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 method of fusing qubits includes providing, to a Hadamard gate: a first qubit; a second qubit; and a Bell pair comprising a fourth qubit that is entangled with a fifth qubit. The method further includes determining whether the Hadamard gate was successful in producing a fused qubit. The method further includes in accordance with the determination that the Hadamard gate was successful in producing fused qubit, outputting the fused qubit.

Abstract: The various embodiments described herein include methods, devices, and systems for fabricating and operating superconducting photon detectors. In one aspect, a photon detector includes: (1) a first waveguide configured to guide photons from a photon source; (2) a second waveguide that is distinct and separate from the first waveguide and optically-coupled to the first waveguide; and (3) a superconducting component positioned adjacent to the second waveguide and configured to detect photons within the second waveguide.

Abstract: The various embodiments described herein include methods, devices, and systems for fabricating and operating superconducting circuitry. In one aspect, an amplification circuit includes: (1) a superconducting component; (2) an amplifier coupled in parallel with the superconducting component such that the superconducting component is in a feedback loop of the amplifier; (3) a voltage source coupled to a first input of the amplifier; (4) one or more resistors coupled to a second input of the amplifier; and (5) an output terminal coupled to an output of the amplifier.

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: 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.

Abstract: A superconductor device is manufactured by depositing a barrier layer over a substrate including silicon, the barrier layer including silicon and nitrogen; depositing a seed layer for a superconductor layer over the barrier layer, the seed layer including aluminum and nitrogen; depositing the superconductor layer over the seed layer, the superconductor layer including a layer of a superconductor material, the barrier layer serving as an oxidation barrier between the layer superconductor material and the substrate; and depositing a silicon cap layer over the superconductor layer. In some embodiments, the superconductor device includes a waveguide and a metal contact at a sufficient distance from the waveguide to prevent optical coupling between the metal contact and the waveguide.

Abstract: A method for removing a native oxide film from a semiconductor substrate includes repetitively depositing layers of germanium on the native oxide and heating the substrate causing the layer of germanium to form germanium oxide, desorbing a portion of the native oxide film. The process is repeated until the oxide film is removed. A subsequent layer of strontium titanate can be deposited on the semiconductor substrate, over either residual germanium or a deposited germanium layer. The germanium can be converted to silicon germanium oxide by exposing the strontium titanate to oxygen.

Abstract: A method includes receiving Bell pairs. Photons are obtained in a Greenberger-Hom-Zeilinger (GHZ) state by providing, to a first beam splitter, a photon from a first Bell pair and a photon from a second Bell pair. The first beam splitter is coupled with a first output channel and a second output channel. Obtaining the photons in the GHZ state further includes providing, to a second beam splitter, a photon from a third Bell pair and a photon from a fourth Bell pair. The second beam splitter is coupled with a third output channel arid a fourth output channel. Obtaining the photons in the GHZ state further includes providing a photon output from the second output channel as a first input to a detector and a photon output in the third output channel a second input to the first detector.

Abstract: An optical device includes a first multi-mode waveguide, a first optical coupler coupled to the first multi-mode waveguide, the first coupler being tapered and curved, and a first single-mode waveguide having a first end coupled to the first optical coupler. The optical device maybe used in an optical delay device. A method of propagating light in a first multi-mode waveguide toward a first optical coupler, propagating the light in the first optical coupler toward a first single-mode waveguide, the first optical coupler being tapered and curved, and propagating the light along the first single-mode waveguide is also disclosed.

Abstract: Electro-optical devices and methods for constructing electro-optical devices such as a switch or phase shifter. An electrode layer is deposited on a substrate layer, a waveguide structure is deposited on the electrode layer, a first cladding layer is deposited on the waveguide structure, and the first cladding layer is planarized and bonded to a wafer. The substrate layer is removed and the electrode layer is etched to split the electrode layer into a first electrode separated from a second electrode. A second cladding layer is deposited on the etched electrode layer. The first and second electrodes may be composed of a material with a large dielectric constant, or they may be composed of a material with a large electron mobility. The device may exhibit a sandwich waveguide architecture where an electro-optic layer is disposed between two strip waveguides.

Abstract: Entanglement among qubits can be generated using “rasterized” and interleaving techniques. A circuit can include a resource state generator that generates one resource state per clock cycle, with each resource state having a number of entangled qubits. The circuit can also include circuits and delay lines to perform entangling measurement operations on qubits of resource states generated by the same resource state generator in different clock cycles. With appropriate selection of delay lines, a single resource state generator can generate all of the resource states needed to generate a large entanglement structure. Hybrid techniques can also be used, where the number of resource state circuits is greater than one but less than the number of resource states needed to generate the entanglement structure.

Abstract: An electronic component having an asymmetric impedance is provided. The component includes first, second and third branches that connect at a common node. The component includes a first portion of superconducting material disposed along the first branch and a second portion of superconducting material disposed along the second branch. The component includes a first device disposed along the first branch and configured to transition the second portion of the superconducting material to a non-superconducting state when a current between a first terminal of the first device and a second terminal of the first device exceeds a first threshold value and a second device disposed along the second branch and configured to transition the first portion of the superconducting material to a non-superconducting state when a current between a first terminal of the second device and a second terminal of the second device exceeds a second threshold value.