Abstract: A temporal multiplexing circuit can include a set of waveguides having different delay lengths, with the waveguides arranged according to a de Bruijn sequence. The set of waveguides can be coupled to a cyclic switch that selectably delivers a group of unsynchronized photons (or other signal pulses) from a contiguous group of input paths into a contiguous group of the delay waveguides. Similarly, a spatial multiplexing circuit can include a set of pairs of waveguides that each implement mode swapping of photons, with different swap distances, with the pairs of waveguides arranged according to a de Bruijn sequence. The set of waveguides can be coupled to a cyclic switch that selectably delivers a group of photons from a set of input paths into a contiguous group of the mode-swap waveguides. Temporal and spatial multiplexing can be combined in a switching network.

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 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: 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 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: A method of forming a film comprises growing, using a deposition system, at least a portion of the film and analyzing, using a RHEED instrument, the at least a portion of the film. Using a computer, data is acquired from the RHEED instrument that is indicative of a stoichiometry of the at least a portion of the film. Using the computer, adjustments to one or more process parameters of the deposition system are calculated to control stoichiometry of the film during subsequent deposition. Using the computer, instructions are transmitted to the deposition system to execute the adjustments of the one or more process parameters. Using the deposition system, the one or more process parameters are adjusted.

Abstract: An optical switch structure includes a substrate, a first electrical contact, and a first material having a first conductivity type electrically connected to the first electrical contact. The optical switch structure also includes a second material having a second conductivity type coupled to the first material, a second electrical contact electrically connected to the second material, and a waveguide structure disposed between the first electrical contact and the second electrical contact. The waveguide structure includes a waveguide core coupled to the substrate and including a core material characterized by a first index of refraction and a waveguide cladding at least partially surrounding the waveguide core and including a cladding material characterized by a second index of refraction less than the first index of refraction and an isotope-enhanced Pockels effect.

Abstract: Techniques disclosed herein relate generally to integrating photonic integrated circuits and electronic integrated circuits in a same package. A device includes a semiconductor substrate and a die stack on the semiconductor substrate. The die stack includes a photonic integrated circuit (PIC) die and an electronic integrated circuit (EIC) die. The PIC die includes a PIC substrate and a photonic integrated circuit formed on the PIC substrate. The EIC die includes an EIC substrate and an electronic integrated circuit formed on the EIC substrate. The EIC die and the PIC die are bonded such that the PIC substrate and the EIC substrate are disposed on opposing sides of the die stack. The PIC substrate is bonded to the semiconductor substrate. The device also includes a cooling plate bonded to the EIC substrate.

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 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 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 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: An expanded Bell state generator can generate a Bell state on four output modes of a set of m output modes, where m is greater than four. Some expanded Bell state generators can receive inputs on any four of a set of 2m input modes. Subsets of the m output modes can be multiplexed to reduce the number of modes to four. According to some embodiments, a set of 2×2 muxes can be used to rearrange the output modes prior to reducing the number of modes.

Abstract: A quantum computing system includes a photon processing system, a photon analyzer, and a photon source module coupled to the photon processing system and to the photon analyzer. The photon source module includes at least one photon source configured to discharge one or more photons per trigger signal and a photon multiplexer configured to direct the one or more photons to the photon processing system or to the photon analyzer.

Abstract: An optical delay device includes a multi-mode waveguide for propagating first light through at least a portion of the multi-mode waveguide. The multi-mode waveguide has a first width. The optical delay device also includes a first waveguide having a second width that is less than the first width and a first coupler connected to the multi-mode waveguide and the first waveguide for coupling the first light from the multi-mode waveguide to the first waveguide. The first waveguide includes a first portion connected to the first coupler for receiving the first light from the first coupler; and a second portion connected to the first portion for receiving the first light from the first portion and positioned adjacent to the multi-mode waveguide for coupling of the first light to the multi-mode waveguide as second light so that the second light propagates through at least the portion of the multi-mode waveguide.

Abstract: A device includes a substrate, a dielectric layer on the substrate, a waveguide within the dielectric layer, and a photodetector optically coupled to the waveguide. The photodetector is disposed above the waveguide layer and is monolithically integrated with the substrate. The photodetector is configured to operate at low temperatures, such as below about 50 K or about 20 K. In some embodiments, the monolithic photonic device includes thermal isolation structures and optical isolation structures. Techniques for manufacturing the monolithic photonic device, including the thermal isolation structures and optical isolation structures, are also described.

Abstract: A method of resolving a number of photons received by a photon detector includes optically coupling a waveguide to a superconducting wire having alternating narrow and wide portions; electrically coupling the superconducting wire to a current source; and electrically coupling an electrical contact in parallel with the superconducting wire. The electrical contact has a resistance less than a resistance of the superconducting wire while at least one narrow portion of the superconducting wire is in a non-superconducting state. The method includes providing to the superconducting wire, from the current source, a current configured to maintain the superconducting wire in a superconducting state in the absence of incident photons; receiving one or more photons via the waveguide; measuring an electrical property of the superconducting wire, proportional to a number of photons incident on the superconducting wire; and determining the number of received photons based on the electrical property.

Abstract: An optical switch structure includes a substrate, a first electrical contact, a first material having a first conductivity type electrically connected to the first electrical contact, a second material having a second conductivity type coupled to the first material, and a second electrical contact electrically connected to the second material. The optical switch structure also includes a waveguide structure disposed between the first electrical contact and the second electrical contact and comprising 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 and a waveguide cladding at least partially surrounding the waveguide core and including a second material characterized by a second index of refraction and a second electro-optic.

Abstract: An electric circuit includes a plurality of superconducting components, each of the plurality of superconducting components having: a respective first terminal; a respective second terminal; and a respective input. The electric circuit further includes a bias current source electrically-connected to the respective first terminal of each of the plurality of superconducting components. The bias current source is configured to provide a bias current adapted to cause the electric circuit to function as a logical OR gate on the respective inputs of the plurality of superconducting components. The electric circuit further includes an output node adapted to output a state of the logical OR gate.