Abstract: A circuit assembly for cooling a quantum electrical device, use of said circuit assembly, a system and a method for cooling a quantum electric device are provided. The circuit assembly comprises a quantum electric device to be cooled, at least one normal-metal-insulator-superconductor (NIS) tunnel junction electrically connected to the quantum electric device and at least one superconductive lead for supplying a drive voltage VQCR for said at least one NIS tunnel junction. The quantum electric device is cooled when the voltage VQCR is supplied to at least one NIS tunnel junction, said voltage VQCR being equal to or below the voltage N?/e, where N=1 or N=2, N is the number of NIS tunnel junctions electrically coupled in series with the means for generating the voltage, ? is the energy gap in the superconductor density of states, and e is the elementary charge.

Abstract: A tunable dissipative circuit is presented for shifting a frequency of a radio frequency signal or microwave signal in a cryogenically cooled environment. One or more couplers make couplings between a propagation path and a tunable resonance element and a controllable dissipator element. A first control input to said tunable resonance element allows changing a resonance frequency of said tunable resonance element with a first control signal. A second control input to said controllable dissipator element allows changing a damping rate of said controllable dissipator element with a second control signal.

Abstract: A three-dimensional superconducting qubit and a method for manufacturing the same are disclosed. In an example, a three-dimensional superconducting qubit comprises a structural base comprising one or more insulating materials, and superconductive patterns on surfaces of the structural base. The superconductive patterns form at least a capacitive part and an inductive part of the three-dimensional superconducting qubit. A first surface of the surfaces of the structural base defines a first plane and a second surface of the surfaces of the structural base defines a second plane, the second plane being oriented differently than the first plane. At least one superconductive pattern of the superconductive patterns extends from the first surface to the second surface.

Abstract: For reading out a state of a qubit, a readout input waveform is injected into a system that comprises an information storage element for storing the state of the qubit and a readout resonator that is electromagnetically coupled to said information storage element. A readout output waveform is extracted from said system and detected. The injection of the readout input waveform takes place through an excitation port that is also used to inject excitation waveforms to the information storage element for affecting the state of the qubit. A phase of the readout input waveform is controllably shifted in the course of injecting it into the system.

Abstract: A quantum processing unit is disclosed. The quantum processing unit includes at least one superconducting qubit based on phase-biased linear and non-linear inductive-energy elements. A superconducting phase difference across the linear and non-linear inductive-energy elements is biased, for example, by an external magnetic field, such that quadratic potential energy terms of the linear and non-linear inductive-energy elements are cancelled at least partly. In a preferred embodiment, such cancellation is at least 30%. The partial cancellation of the quadratic potential makes it possible to implement a high-coherence high-anharmonicity superconducting qubit design.

Abstract: A quantum processing unit is disclosed. The quantum processing unit includes at least one superconducting qubit that is based on phase-biased linear and non-linear inductive-energy elements. A superconducting phase difference across the linear and non-linear inductive-energy elements is biased, for example, by an external magnetic field, such that quadratic potential energy terms of the linear and non-linear inductive-energy elements are cancelled at least partly. In a preferred embodiment, such cancellation is at least 30%. The partial cancellation of the quadratic potential energy terms makes it possible to implement a high-coherence high-anharmonicity superconducting qubit design.

Abstract: An arrangement, an apparatus, a quantum computing system, and a method are disclosed for reducing qubit leakage errors. In an example, an apparatus includes a qubit having a ground state and a plurality of excited states. The plurality of excited states include a lowest excited state. An energy difference between the ground state and the lowest excited state corresponds to a first frequency, and an energy difference between the lowest excited state and another excited state in the plurality of excited states corresponds to a second frequency. The apparatus also includes an energy dissipation structure to dissipate transferred energy, and a filter having a stopband and a passband. The filter is coupled to the qubit and to the energy dissipation structure. The stopband includes the first frequency and the passband includes the second frequency for reducing qubit leakage errors.

Abstract: An arrangement, an apparatus, a quantum computing system, and a method are disclosed for reducing qubit leakage errors. In an example, an apparatus includes a qubit having a ground state and a plurality of excited states. The plurality of excited states include a lowest excited state. An energy difference between the ground state and the lowest excited state corresponds to a first frequency, and an energy difference between the lowest excited state and another excited state in the plurality of excited states corresponds to a second frequency. The apparatus also includes an energy dissipation structure to dissipate transferred energy, and a filter having a stopband and a passband. The filter is coupled to the qubit and to the energy dissipation structure. The stopband includes the first frequency and the passband includes the second frequency for reducing qubit leakage errors.

Abstract: It is an objective to provide an arrangement for reducing qubit leakage errors in a quantum computing system. According to an embodiment, an arrangement for reducing qubit leakage errors includes a first qubit and a second qubit selectively couplable to each other. The arrangement also includes an energy dissipation structure that is selectively couplable to the first qubit. The energy dissipation structure is configured to dissipate energy transferred from the first qubit. The arrangement further includes a control unit configured to perform a first quantum operation to transfer a property of a quantum state from the first qubit to the second qubit, couple the first qubit to the energy dissipation structure for a time interval, and perform a second quantum operation to transfer the property of the quantum state from the second qubit to the first qubit after the time interval.

Abstract: A detector of microwave radiation includes a signal input and a detector output. An absorber element of ohmic conductivity is coupled to said signal input through a first length of superconductor. A variable impedance element, the impedance of which is configured to change as a function of temperature, is coupled to the detector output through a second length of superconductor. The detector also includes a heating input and a heating element coupled to the heating input through a third length of superconductor. The absorber element, the variable impedance element, and the heating element are coupled to each other through superconductor sections of lengths shorter than any of said first, second, and third lengths of superconductor.

Abstract: A quantum processing unit is disclosed. The quantum processing unit includes at least one superconducting qubit that is based on phase-biased linear and non-linear inductive-energy elements. A superconducting phase difference across the linear and non-linear inductive-energy elements is biased, for example, by an external magnetic field, such that quadratic potential energy terms of the linear and non-linear inductive-energy elements are cancelled at least partly. In a preferred embodiment, such cancellation is at least 30%. The partial cancellation of the quadratic potential energy terms makes it possible to implement a high-coherence high-anharmonicity superconducting qubit design.

Abstract: A vector signal generator is capable of operating on microwave frequencies. It comprises a microwave resonator, an output for coupling microwave photons out of said microwave resonator, and a Josephson junction or junction array coupled to the microwave resonator for emitting microwave signals into the microwave resonator. A biasing circuit is provided for applying a bias to the Josephson junction or junction array. A tunable attenuator is coupled to said microwave resonator.

Abstract: It is an objective to provide an arrangement and a quantum computing system for qubit readout. According to an embodiment, an arrangement for qubit readout includes at least one qubit and a controllable energy relaxation structure comprising at least one junction. The controllable energy relaxation structure is coupled to the at least one qubit, and is configured to absorb, in response to a control signal, at least one photon from the at least one qubit via photon-assisted tunnelling of a charge through the at least one junction. The arrangement also includes a charge storage configured to store the tunnelled charge and a charge sensing structure coupled to the charge storage. The charge sensing structure is configured to provide a readout signal in response to detecting the tunnelled charge in the charge storage.

Abstract: A three-dimensional superconducting qubit and a method for manufacturing the same are disclosed. In an example, a three-dimensional superconducting qubit comprises a structural base comprising one or more insulating materials, and superconductive patterns on surfaces of the structural base. The superconductive patterns form at least a capacitive part and an inductive part of the three-dimensional superconducting qubit. A first surface of the surfaces of the structural base defines a first plane and a second surface of the surfaces of the structural base defines a second plane, the second plane being oriented differently than the first plane. At least one superconductive pattern of the superconductive patterns extends from the first surface to the second surface.

Abstract: A circuit assembly for cooling a quantum electrical device, use of said circuit assembly, a system and a method for cooling a quantum electric device are provided. The circuit assembly comprises a quantum electric device to be cooled, at least one normal-metal-insulator-superconductor (NIS) tunnel junction electrically connected to the quantum electric device and at least one superconductive lead for supplying a drive voltage VQCR for said at least one NIS tunnel junction. The quantum electric device is cooled when the voltage VQCR is supplied to at least one NIS tunnel junction, said voltage VQCR being equal to or below the voltage N?/e, where N=1 or N=2, N is the number of NIS tunnel junctions electrically coupled in series with the means for generating the voltage, ? is the energy gap in the superconductor density of states, and e is the elementary charge.

Abstract: A quantum computing circuit is disclosed herein. An example quantum computing circuit includes a first chip with at least one qubit thereon. The quantum computing circuit also includes a second chip with at least other quantum circuit elements other than qubits thereon. The first chip and the second chip are stacked together in a flip-chip configuration and attached to each other with bump bonding that includes bonding bumps.

Abstract: It is an objective to provide an arrangement for reducing qubit leakage errors in a quantum computing system. According to an embodiment, an arrangement for reducing qubit leakage errors includes a first qubit and a second qubit selectively couplable to each other. The arrangement also includes an energy dissipation structure that is selectively couplable to the first qubit. The energy dissipation structure is configured to dissipate energy transferred from the first qubit. The arrangement further includes a control unit configured to perform a first quantum operation to transfer a property of a quantum state from the first qubit to the second qubit, couple the first qubit to the energy dissipation structure for a time interval, and perform a second quantum operation to transfer the property of the quantum state from the second qubit to the first qubit after the time interval.

Abstract: An arrangement, an apparatus, a quantum computing system, and a method are disclosed for reducing qubit leakage errors. In an example, an apparatus includes a qubit having a ground state and a plurality of excited states. The plurality of excited states include a lowest excited state. An energy difference between the ground state and the lowest excited state corresponds to a first frequency, and an energy difference between the lowest excited state and another excited state in the plurality of excited states corresponds to a second frequency. The apparatus also includes an energy dissipation structure to dissipate transferred energy, and a filter having a stopband and a passband. The filter is coupled to the qubit and to the energy dissipation structure. The stopband includes the first frequency and the passband includes the second frequency for reducing qubit leakage errors.

Abstract: A method, system, and arrangement for resetting qubits are disclosed. An example system includes one or more quantum circuit refrigerators for resetting qubits. Each of the quantum circuit refrigerators includes a tunneling junction and a control input for receiving a control signal. Photon-assisted single-electron tunneling takes place across the respective tunneling junction in response to a control signal. Capacitive or inductive coupling elements between the qubits and the quantum circuit refrigerators couple each qubit to the quantum circuit refrigerator(s). The qubits, quantum circuit refrigerators, and coupling elements are located in a cryogenically cooled environment. A common control signal line to the control inputs crosses into the cryogenically cooled environment from a room temperature environment.

Abstract: A circuit assembly for cooling a quantum electrical device, use of said circuit assembly, a system and a method for cooling a quantum electric device are provided. The circuit assembly comprises a quantum electric device to be cooled, at least one normal-metal-insulator-superconductor (NIS) tunnel junction electrically connected to the quantum electric device and at least one superconductive lead for supplying a drive voltage VQCR for said at least one NIS tunnel junction. The quantum electric device is cooled when the voltage VQCR is supplied to at least one NIS tunnel junction, said voltage VQCR being equal to or below the voltage N?/e, where N=1 or N=2, N is the number of NIS tunnel junctions electrically coupled in series with the means for generating the voltage, ? is the energy gap in the superconductor density of states, and e is the elementary charge.