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.

Abstract: A quantum computing system and methods for performing fault-tolerant quantum computing. A fusion controller sequentially performs a series of fusion measurements on different fusion sites of a plurality of fusion sites to obtain a respective series of classical measurement results. The series of fusion measurements is performed on quantum modes of a logical qubit. For respective fusion measurements of the series of fusion measurements, a basis for performing the respective fusion measurement is selected based on classical measurement results of previous fusion measurements. The series of classical measurement results are in the memory medium.

Abstract: A programmable circuit includes a superconducting component arranged in a multi-dimensional array of alternating narrow and wide portions. The programmable circuit further includes a plurality of heat sources, each heat source configured to selectively provide heat to a respective narrow portion sufficient to transition the respective narrow portion from a superconducting state to a non-superconducting state. The programmable circuit further includes a plurality of electrical terminals, each electrical terminal coupled to a respective wide portion of the multi-dimensional array.

Abstract: A multirail-encoded qubit can be implemented using a quantum system having a state space that includes a number M of distinct modes, where M is an integer greater than 2. The M modes are logically partitioned into two disjoint subsets (or “bands”), with each mode assigned to exactly one of the bands. The multirail encoding is defined such that a state in which any one of the modes in the first band is occupied and all modes in the second band are unoccupied maps to a logical 0 state of the qubit, and a state in which any one of the modes in the second band is occupied and all modes of the first band are unoccupied maps to a logical 1 state. Systems and methods for generating, measuring, and operating on multirail-encoded qubits are disclosed.

Abstract: Circuits for generating a pair of qudits in a maximally entangled state and methods of operating such circuits are disclosed. The circuits can be photonic circuits that use a combination of beam splitters, phase shifters, and detectors to produce an entangled pair of d-dimensional qudits from an input set of 4d photons. In a case where d equals 2, a pair of qubits in a Bell state can be generated.

Abstract: An entangled quantum system can be generated using entanglement-generating circuits that operate non-deterministically. Multiple instances of the entanglement generating circuit can be operated and outputs of successful instances can be propagated. The circuit can be implemented such that a photon that is part of the final output state passes through as few as one or two active switches from generation to the final output state.

Abstract: An optical switch device includes a first semiconductor structure configured to operate as a first waveguide and a second semiconductor structure configured to operate as a second waveguide. The second semiconductor structure is located above or below the first semiconductor structure and separated from the first semiconductor structure. The second semiconductor structure includes a portion of a first doped region doped with dopants of a first type and a portion of a second doped region doped with dopants of a second type that is different from the dopants of the first type.

Abstract: A photon detector is provided. The photon detector includes a superconducting wire having a plurality of alternating narrow and wide portions; a current source electrically-coupled to the superconducting wire and configured to supply the superconducting wire with electrical current; and an optical waveguide optically coupled to the plurality of narrow portions of the superconducting wire.

Abstract: A quantum computing system and methods for performing fusion based quantum computing on encoded qubits. A fusion controller sequentially performs a series of fusion measurements on respective physical qubits of first and second encoded qubits to obtain a respective series of classical measurement results. For respective fusion measurements of the series of fusion measurements, a basis for performing the respective fusion measurement is selected based on classical measurement results of previous fusion measurements. An encoded fusion measurement result is determined based on the classical measurement results, and the encoded fusion measurement result is stored in a memory medium.

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: 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: 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: The various embodiments described herein include methods, devices, and systems for fabricating and operating diodes. In one aspect, an electrical circuit includes: (1) a diode component having a particular energy band gap; (2) an electrical source electrically coupled to the diode component and configured to bias the diode component in a particular state; and (3) a heating component thermally coupled to a junction of the diode component and configured to selectively supply heat corresponding to the particular energy band gap.

Abstract: A transistor includes (i) a first wire including a semiconducting component configured to operate in an on state at temperatures above a semiconducting threshold temperature and (ii) a second wire including a superconducting component configured to operate in a superconducting state while: a temperature of the superconducting component is below a superconducting threshold temperature and a first input current supplied to the superconducting component is below a current threshold. The semiconducting component is located adjacent to the superconducting component. In response to a first input voltage, the semiconducting component is configured to generate an electromagnetic field sufficient to lower the current threshold such that the first input current exceeds the lowered current threshold.

Abstract: An optical coupler includes a first waveguide including a first multi-mode waveguide section having a cross-section characterized by a first height and a first width that is greater than the first height and a second waveguide including a second multi-mode waveguide section having a cross-section characterized by a second height and a second width that is greater than the second height. The first multi-mode waveguide section is positioned adjacent to the second multi-mode waveguide section at least partially above or below the second multi-mode waveguide so that light entering the first multi-mode waveguide section is coupled from the first multi-mode waveguide section to the second multi-mode waveguide section. Methods for coupling light between waveguides with the optical coupler and optical devices that include the optical coupler are also described.

Abstract: A device includes a first semiconductor layer; a portion of a second semiconductor layer disposed on the first semiconductor layer; and a third semiconductor layer including a first region disposed on the portion of the second semiconductor layer and a second region disposed on the first semiconductor layer. A thickness of the first region is less than a predefined thickness. The device also includes an etch stop layer disposed on the third semiconductor layer; a plurality of distinct portions of a fourth semiconductor layer disposed on the etch stop layer and exposing one or more distinct portions of the etch stop layer over the portion of the second semiconductor layer; and a plurality of distinct portions of a superconducting layer disposed on the plurality of distinct portions of the fourth semiconductor layer and the exposed one or more distinct portions of the etch stop layer.

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: A device includes a plurality of photon sources coupled to a plurality of output terminals. The plurality of photon sources are coupled together, by a first switch layer, into a plurality of photon source groups. The first switch layer comprises a plurality of switches. The device further includes a second switch layer coupled to output terminals of the first switch layer. The second switch layer includes a plurality of second layer n-by-n switches and a plurality of second layer l-by-l switches, wherein l is less than n. At least two output terminals from two respective photon sources residing within a first photon source group of the plurality of photon source groups and a second photon source group of the plurality of photon source groups are coupled directly to respective output terminals of the device without being coupled to any intervening second switch from the second switch layer.