BACKGROUND

Technical Field

The present disclosure generally relates to superconducting devices, and more particularly, qubit control.

Description of the Related Art

Superconducting quantum computing is an implementation of a quantum computer in superconducting electronic circuits. Quantum computation studies the application of quantum phenomena for information processing and communication. Various models of quantum computation exist, and the most popular models include the concepts of qubits and quantum gates. A qubit is a generalization of a bit that has two possible states, but can be in a quantum superposition of both states. A quantum gate is a generalization of a logic gate, however the quantum gate describes the transformation that one or more qubits will experience after the gate is applied on them, given their initial state.

SUMMARY

According to various embodiments, a system and quantum circuit structure are provided for reducing cross-talk between circuit elements that are on different planes. A first quantum circuit plane includes a first qubit, a second qubit, and a coupled-line bus coupled between a first qubit and a second qubit. There is a third qubit. A second circuit plane, sometimes referred to herein as an interposer chip, is connected to the first quantum circuit plane and includes a control line that is coupled to the third qubit. The control line and the coupled-line bus are on different planes and crossing over each other and configured to mitigate cross talk caused by the crossing during signal transmission.

In one embodiment, the coupled-line bus is configured to transmit differential mode signals between the first and second qubits of the first quantum circuit plane.

In one embodiment, the first quantum circuit plane and the second circuit plane are located on separate chips of a flip chip and connected together via bump bonds.

In one embodiment, the control line is a feed line that is configured to transmit a signal to drive the third qubit.

In one embodiment, the control line is a resonator that is configured to read a signal from the third qubit.

In one embodiment, the control line is orthogonal to the coupled-line bus at the crossing to suppress an inductive coupling between the control line and the coupled-line bus.

In one embodiment, the coupled-line bus is a dual strip coplanar waveguide (CPW) transmission-line resonator.

In one embodiment, the first qubit and the second qubit are coupled to the coupled-line bus differentially and configured to excite only an odd mode of the coupled-line bus.

In one embodiment, a wavelength of a qubit excitation in the control line is longer than a width and a gap of the coupled-line bus.

In one embodiment, a suppression ratio of a crosstalk between the coupled-line bus and the control line depends on a gap between lines of the coupled-line bus.

According to one embodiment, a method of reducing crosstalk between different circuit planes of a quantum circuit, such as a qubit chip and an interposer chip, is provided. A coupled-line bus is provided between a first qubit and a second qubit of a first quantum circuit plane. A control line is provided on a second circuit plane. The control line connects to a third qubit. The first circuit plane can be on a first quantum circuit plane, the second circuit plane can be on a second circuit plane, and the first quantum circuit plane is bonded to the second circuit plane such that the control line and the coupled-line bus are on different planes and crossing over each other and mitigate cross talk caused by the crossing during signal transmission.

In one embodiment, differential mode signals are transmitted between the first and second qubits of the first quantum circuit plane.

In one embodiment, the first quantum circuit plane and the second circuit plane are on different chips, and the chips are coupled (e.g., bonded or connected) together via bump bonds.

In one embodiment, the control line is a feed line and the third qubit is driven through the feed line.

In one embodiment, a common mode signal is generated on the coupled-line bus to electrically mitigate a cross talk from the control line to the coupled-line bus.

In one embodiment, an inductive coupling between the control line and the coupled-line bus is suppressed by arranging the control line to be orthogonal to the coupled-line bus.

In one embodiment, the first qubit and the second qubit are coupled to the coupled-line bus differentially to excite only an odd mode of the coupled-line bus.

By virtue of the features discussed herein, classical crosstalk between a first quantum circuit plane and a second circuit plane, such as a qubit chip and an interposer chip in a flip chip geometry, is substantially reduced. These and other features will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

