Abstract: There is described a method for performing a two-qubit gate. The method comprises coupling a first qubit to a second qubit, and coupling a third qubit to the first qubit and to the second qubit, wherein the third qubit is a coupler. A drive signal is applied to the coupler to perform the two-qubit gate on the first qubit and the second qubit by driving the coupler, the drive signal creating coupling between eigenstates of a Hamiltonian of the coupler.

Abstract: A dilution refrigerator, such as for a quantum computing system, includes a cryostat having a plurality of temperature-controlled flanges inside a vacuum chamber. A dilution unit is disposed inside the cryostat and operable to cool a first group of the flanges. A continuous flow helium refrigerator is in heat transfer communication with a lowest temperature flange of a second group of flanges, disposed at progressively lower temperatures that are greater than those of the first group of flanges, to provide primary cooling thereto to a first temperature. The continuous flow helium refrigerator resides at least partially in the cryostat and includes a helium liquefier and a first closed-loop circuit thermally coupling the helium liquefier to the lowest temperature flange of the second group of flanges. The helium liquefier provides liquid helium to the lowest temperature flange of the second group of flanges via the first closed-loop circuit.

Abstract: There is described herein a topologically protected quantum circuit with superconducting qubits and method of operation thereof. The circuit comprises a plurality of physical superconducting qubits and a plurality of coupling devices interleaved between pairs of the physical superconducting qubits. The coupling devices comprise at least one ?-Josephson junction, wherein a Josephson phase ?0 of the ?-Josephson junction is non-zero in a ground state, the coupling devices have a Josephson energy EJ?, the physical superconducting qubits have a Josephson energy EJq, and the circuit operates in a topological regime when E J ? q 2 > - E J ? ? ? cos ? ? 0 > E J ? q 3 .

Abstract: There is described herein a quantum computing system, quantum processor, and method of operating a quantum computing system. The quantum computing system comprises a quantum control system configured for at least one of delivery and receipt of multiplexed optical signals. At least one optical fiber is coupled to the quantum control system for carrying the multiplexed optical signals, and a quantum processor is disposed inside a cryogenics apparatus and coupled to the at least one optical fiber. The quantum processor comprises: at least one converter configured for converting between the multiplexed optical signals and microwave signals at different frequencies; and a plurality of solid-state quantum circuit elements coupled to the at least one converter and addressable by respective ones of the microwave signals at different frequencies.

Abstract: A cryostat, such as for a quantum computing system, includes a plurality of temperature-controlled flanges operable to be cooled to respective cryogenic target temperatures, the temperature-controlled flanges being nested one inside another and concentrically arranged about a central axis. The temperature-controlled flanges are radially spaced apart and define closed polygonal perimeters. The temperature-controlled flanges including an outermost flange defining a vacuum chamber, an innermost flange enclosing a central core of the cryostat, and intermediate flanges radially located between the innermost flange and the outermost flange. Each of the intermediate flanges surrounds one or more of the other temperature-controlled flanges. The outermost flange is maintained at a highest temperature, the innermost flange is maintained at a lowest temperature, and the intermediate flanges are maintained at respective intermediate temperatures less than the highest temperature and greater than the lowest temperature.

Abstract: There is described herein a quantum computing system, quantum processor, and method of operating a quantum computing system. The quantum computing system comprises a quantum control system configured for at least one of delivery and receipt of multiplexed optical signals. At least one optical fiber is coupled to the quantum control system for carrying the multiplexed optical signals, and a quantum processor is disposed inside a cryogenics apparatus and coupled to the at least one optical fiber. The quantum processor comprises: at least one converter configured for converting between the multiplexed optical signals and microwave signals at different frequencies; and a plurality of solid-state quantum circuit elements coupled to the at least one converter and addressable by respective ones of the microwave signals at different frequencies.

Abstract: An apparatus and method for molecular beam epitaxy are described herein. The apparatus comprises an enclosure defining a vacuum chamber. A substrate holder is mounted within the vacuum chamber. At least one molecular beam source is in fluid communication with the vacuum chamber. A cooling shroud having at least one surface is mounted within the vacuum chamber spaced from the substrate holder. A cryocooler having at least a portion extending into the vacuum chamber is operatively coupled to the cooling shroud for extracting heat therefrom, and cooling the at least one surface of the cooling shroud to cryogenic temperatures.

Abstract: There is described a microwave device and methods of operating same. The device comprises at least one superconducting qubit coupled to a transmission line defining a first port, and a filter. The filter comprises a first resonant element having a first resonance frequency f1, positioned along the transmission line between the first port and the qubit, and a second resonant element having a second resonance frequency f2 different from f1 and positioned along the transmission line between the first resonant element and the qubit.

Abstract: A qubit circuit and a method for topological protection of a qubit circuit are described. The circuit comprises a plurality of physical superconducting qubits and a plurality of coupling devices interleaved between pairs of the physical superconducting qubits. The coupling devices are tunable to operate the qubit circuit either in a topological regime or as a series of individual physical qubits. At least two superconducting loops, each one threadable by an external flux, are part of the qubit circuit.