Abstract: A method for processing a substrate includes positioning a silicon substrate in a deposition chamber. One or more intermediate layers are deposited on a surface of the silicon. The one or more intermediate layers can include strontium, which combines with the silicon to form strontium silicide. Alternatively, the one or more intermediate layers comprise germanium. A layer of amorphous strontium titanate is deposited on the one or more intermediate layers in a transient environment in which oxygen pressure is reduced while temperature is increased. The substrate is then exposed to an oxidizing and annealing atmosphere that oxidizes the one or more intermediate layers and converts the layer of amorphous strontium titanate to crystalline strontium titanate.

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 photon detecting component is provided. The photon detecting component includes a first waveguide and a detecting section. The detecting section includes a second waveguide; a detector, optically coupled with the second waveguide, configured to detect one or more photons in the second waveguide; an optical switch configured to provide an optical coupling between the first waveguide and the second waveguide when the detector is operational; and an electrical switch electrically coupled to the detector, wherein the electrical switch is configured to change state in response to the detector detecting one or more photons. The photon detecting component further includes readout circuitry configured to determine a state of the electrical switch of the detecting section.

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 photon source module includes a plurality of photon sources, wherein each photon source is configured to non-deterministically generate one or more non-entangled or entangled photons in response to receiving a trigger signal. When two or more photon sources simultaneously generate photons in response to a trigger signal, one photon of a first photon pair is directed to a photon processing system and one photon of a second photon pair is directed to a photon analyzer. During repetitive operation, the photon analyzer analyzes photons from each of the plurality of photon sources to determine characteristics of each photon source and can use that information to direct the highest quality photons to the photon processing system.

Abstract: The various embodiments described herein include methods, devices, and circuits for reducing switch transition time of superconductor switches. In some embodiments, an electrical circuit includes: (i) an input component configured to generate heat in response to an electrical input; and (ii) a first superconducting component thermally-coupled to the input component. The electrical circuit is configured such that, in the absence of the electrical input, at least a portion of the first superconducting component is maintained in a non-superconducting state in the absence of the electrical input; and, in response to the electrical input, the first superconducting component transitions to a superconducting state.

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: An optical phase shift circuit can include: a first Mach Zehnder lattice and a second Mach Zehnder lattice. Each Mach Zehnder lattice can have a first waveguide and a second waveguide, with a set of active phase shifters disposed along one of the waveguides and a plurality of directional coupler regions disposed along both waveguides between the active phase shifters. A first passive phase shifter can be coupled between one output path of the first Mach Zehnder lattice and one input path of the second Mach Zehnder lattice, and a second passive phase shifter can be coupled between the other output path of the first Mach Zehnder lattice and the other input path of the second Mach Zehnder lattice. Optical phase shift circuits of this kind can be used to implement phase shifters in a Generalized Mach Zehnder interferometer.

Abstract: In some embodiments method comprises depositing a ferroelectric layer on a top surface of a semiconductor wafer and forming one or more gaps in the ferroelectric layer. The one or more gaps can be formed on a repetitive spacing to relieve stresses between the ferroelectric layer and the semiconductor wafer. A first dielectric layer is deposited over the ferroelectric layer and the first dielectric layer is planarized to fill in the gaps. A second dielectric layer is formed between the ferroelectric layer and the semiconductor wafer. The second dielectric layer can be formed by annealing the wafer in an oxidizing atmosphere such that an upper portion of the semiconductor substrate forms an oxide layer between the semiconductor substrate and the ferroelectric layer.

Abstract: A quantum computing system for converting Pauli errors of one or more qubits to erasure errors in a photonic quantum computing architecture. Two or more photonic qubits may be input to a quantum computing system, where at least one first qubit of the two or more qubits has experienced a Pauli error. A sequence of linear optical circuitry operations may be performed on the two or more qubits to generate two or more modified qubits, wherein the sequence of operations transforms one or more of the first qubits from a logical subspace of a Fock space to an erasure subspace of the Fock space. A cluster state for universal quantum computing may be generated from the two or more modified qubits using probabilistic entangling gates. A quantum computational algorithm may be performed using the quantum cluster state generated from the two or more modified qubits.

Abstract: Photons can propagate concurrently in two different directions along optical paths in a generalized Mach Zehnder interferometer (GMZI). A counterpropagating GMZI can include a first set of input ports and a second set of input ports, a first set of output ports and a second set of output ports, and optical components interconnected to form a GMZI that can selectably establish a first optical path between one of the the first set of input ports and one of the first set of output ports and a second optical path between one of the second set of input ports and one of the second set of output ports. The first optical path and the second optical path can include an overlapping portion though which photons on the first and second optical paths propagate in opposing directions.

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: 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 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: A system includes a plurality of wafer-scale modules and a plurality of optical fibers. Each wafer-scale module includes an optical backplane and one or more die stacks on the optical backplane. The optical backplane includes a substrate and at least one optical waveguide layer configured to transport and/or manipulate photonic quantum systems (e.g., photons, qubits, qudits, large entangled states, etc.). Each die stack of the one or more die stacks includes a photonic integrated circuit (PIC) die optically coupled to the at least one optical waveguide layer of the optical backplane. The plurality of optical fibers is coupled to the optical backplanes of the plurality of wafer-scale modules to provide inter-module and/or intra-module interconnects for the photonic quantum systems.

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.