Abstract: A superconducting circuit comprises a first and second magnetic-flux-tunable elements. Each of these has a respective flux-sensitive part. First and second current-driven superconductive on-chip flux bias lines are provided. Each of these passes adjacent to the flux-sensitive part of the respective magnetic-flux-tunable element. A first plurality of superconductive stray current paths exists adjacent to the first magnetic-flux-tunable element. A second plurality of superconductive stray current paths exist adjacent to the second magnetic-flux-tunable element. The superconductive stray current paths distribute stray currents originating from the flux line of the other magnetic-flux-tunable element into a respective plurality of stray currents around the respective magnetic-flux-tunable element. This way the stray currents are kept from changing the electric characteristics of the respective magnetic-flux-tunable element.

Abstract: The invention is generally related to the field of quantum computing and particularly to a tunable resonator-resonator coupling circuit that provides both direct and indirect couplings between linear or nonlinear resonators. The indirect coupling is provided by using a tunable coupling element that comprises two ungrounded superconducting islands. Since the superconducting islands are ungrounded, it is possible to provide different signs of coupling frequencies for the resonators and the superconducting islands, which in turn allows the interaction between the first and second resonators to be controlled more efficiently. Moreover, the design, calibration, and operation of the circuit with such a tunable coupling element are significantly easier and simpler compared to the existing analogues, while providing the same or even better performance. A quantum computing apparatus using one or more such circuits is also provided.

Abstract: A superconducting circuit comprises a first and second magnetic-flux-tunable elements. Each of these has a respective flux-sensitive part. First and second current-driven superconductive on-chip flux bias lines are provided. Each of these passes adjacent to the flux-sensitive part of the respective magnetic-flux-tunable element. A first plurality of superconductive stray current paths exists adjacent to the first magnetic-flux-tunable element. A second plurality of superconductive stray current paths exist adjacent to the second magnetic-flux-tunable element. The superconductive stray current paths distribute stray currents originating from the flux line of the other magnetic-flux-tunable element into a respective plurality of stray currents around the respective magnetic-flux-tunable element. This way the stray currents are kept from changing the electric characteristics of the respective magnetic-flux-tunable element.

Abstract: The invention is generally related to the field of quantum computing and particularly to a tunable resonator-resonator coupling circuit that provides both direct and indirect couplings between linear or nonlinear resonators. The indirect coupling is provided by using a tunable coupling element that comprises two ungrounded superconducting islands. Since the superconducting islands are ungrounded, it is possible to provide different signs of coupling frequencies for the resonators and the superconducting islands, which in turn allows the interaction between the first and second resonators to be controlled more efficiently. Moreover, the design, calibration, and operation of the circuit with such a tunable coupling element are significantly easier and simpler compared to the existing analogues, while providing the same or even better performance. A quantum computing apparatus using one or more such circuits is also provided.

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: 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 tunable coupler for making a controllable coupling to at least a first qubit is disclosed. The tunable coupler includes a first constant coupling element and a tunable coupling element. The first constant coupling element forms a non-galvanic coupling interface to at least the first qubit at a first extremity that is distant from the tunable coupling element. The tunable coupling element is located adjacent to a non-galvanic coupling interface formed as an interface to a circuit element at a second extremity thereof.

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 sample cell is provided for holding a sample to be placed in a cryogenically cooled environment. The sample cell comprises an airtight, openable and closable enclosure. Within said enclosure is a sample base for receiving the sample. A refrigerator attachment is provided for attaching the sample cell to a refrigerated body of a cryogenically cooled environment. The sample cell comprises a thermal connection between the sample base and the refrigerator attachment. One or more air-tight connectors are provided for establishing electric connections between inside and outside of said enclosure.