Tunable qubit device in a superconducting quantum processing circuit
In a general aspect, a superconducting quantum processing circuit includes a tunable qubit device. The tunable qubit device includes a circuit loop configured to receive, during operation of the tunable qubit device, a magnetic flux that controls a qubit frequency of the tunable qubit device. In some aspects, the circuit loop consists of: a single non-linear circuit element and one or more linear circuit elements. The single non-linear circuit element is a Josephson junction connected between a first circuit node and a second circuit node. The one or more linear circuit elements includes a linear inductor connected in parallel with the Josephson junction between the first circuit node and the second circuit node.
1 . A superconducting quantum processing circuit comprising:
a tunable qubit device, wherein the tunable qubit device is a tunable-frequency transmon qubit device comprising a circuit loop configured to receive, during operation of the tunable qubit device, a magnetic flux that controls a qubit frequency of the tunable qubit device, the circuit loop consisting of:
a single non-linear circuit element, the single non-linear circuit element being a Josephson junction connected between a first circuit node and a second circuit node; and
one or more linear circuit elements, the one or more linear circuit elements comprising a linear inductor connected in parallel with the Josephson junction between the first circuit node and the second circuit node, wherein the linear inductor is a conductive stripline, and the conductive stripline is a superconducting material formed as a straight line.
2 . The superconducting quantum processing circuit of claim 1 , wherein the conductive stripline is a superconducting wire.
3 . The superconducting quantum processing circuit of claim 1 , wherein the conductive stripline is a superconducting wire with non-negligible kinetic inductance.
4 . The superconducting quantum processing circuit of claim 1 , wherein the tunable qubit device comprises two qubit electrodes, the two qubit electrodes are electrically floating and are conductively connected to the first and second circuit nodes, respectively.
5 . The superconducting quantum processing circuit of claim 1 , wherein the tunable qubit device comprises two qubit electrodes, the two qubit electrodes are conductively connected to the first and second circuit nodes, respectively, and one of the two qubit electrodes is conductively connected to ground.
6 . The superconducting quantum processing circuit of claim 1 , wherein the tunable qubit device comprises two qubit electrodes, the two qubit electrodes are capacitively connected to ground and are conductively connected to the first and second circuit nodes, respectively.
7 . The superconducting quantum processing circuit of claim 1 , further comprising:
a flux bias control line associated with the tunable qubit device, the flux bias control line comprising a flux bias device configured to generate the magnetic flux that controls the qubit frequency of the tunable qubit device.
8 . The superconducting quantum processing circuit of claim 1 , wherein the linear inductor has an inductance in a range between 1 and 10 nanoHenry (nH).
9 . The superconducting quantum processing circuit of claim 1 , wherein the linear inductor has an inductance in a range between 3 and 6 nH.
10 . The superconducting quantum processing circuit of claim 1 , wherein the linear inductor has an inductance in a range between 3 and 8 nH.
11 . The superconducting quantum processing circuit of claim 1 , wherein the qubit frequency of the tunable qubit device is in a range between 1 and 10 GigaHertz (GHz).
12 . A quantum computing method comprising:
operating a superconducting quantum processing circuit comprising a tunable qubit device, wherein the tunable qubit device is a tunable-frequency transmon qubit device comprising a circuit loop consisting of:
a single non-linear circuit element, the single non-linear circuit element being a Josephson junction connected between a first circuit node and a second circuit node; and
one or more linear circuit elements, the one or more linear circuit elements comprising a linear inductor connected in parallel with the Josephson junction between the first circuit node and the second circuit node, wherein the linear inductor is a conductive stripline, and the conductive stripline is a superconducting material formed as a straight line, and
wherein operating the superconducting quantum processing circuit comprises applying, to the circuit loop of the tunable qubit device, a magnetic flux that controls a qubit frequency of the tunable qubit device.
13 . The method of claim 12 , wherein the superconducting quantum processing circuit comprises a flux bias device associated with the tunable qubit device, and applying the magnetic flux to the circuit loop comprises generating the magnetic flux by operation of the flux bias device.
14 . The method of claim 13 , wherein generating the magnetic flux by operation of the flux bias device comprises:
generating a flux bias control signal by operation of a control system; and
delivering the flux bias control signal to the flux bias device.
15 . The method of claim 14 , wherein the superconducting quantum processing circuit comprises a flux bias control line communicably coupled to the flux bias device, and delivering the flux bias control signal to the flux bias device comprises:
delivering the flux bias control signal to the flux bias device via the flux bias control line.
16 . The method of claim 14 , wherein operating the superconducting quantum processing circuit comprises applying a qubit drive signal to the tunable qubit device.
17 . The method of claim 16 , wherein the superconducting quantum processing circuit comprises a qubit drive line, and applying the qubit drive signal to the tunable qubit device comprises:
delivering the qubit drive signal to the tunable qubit device via the qubit drive line.
18 . The method of claim 16 , wherein the flux bias control signal is configured to tune the magnetic flux applied to the tunable qubit device between a parking value and a gate-activating value.
19 . The method of claim 18 , wherein operating the superconducting quantum processing circuit comprises activating a single-qubit quantum logic gate on the tunable qubit device by:
applying the qubit drive signal at a qubit drive frequency; and
tuning the magnetic flux to the gate-activating value.
20 . The method of claim 12 , wherein operating the superconducting quantum processing circuit comprises applying a quantum logic gate to a qubit defined by the tunable qubit device, and applying the quantum logic gate comprises applying the magnetic flux to the circuit loop.
21 . A quantum computing system comprising:
a superconducting quantum processing circuit comprising:
a tunable qubit device, wherein the tunable qubit device is a tunable-frequency transmon qubit device comprising a circuit loop configured to receive, during operation of the tunable qubit device, a magnetic flux that controls a qubit frequency of the tunable qubit device, the circuit loop consisting of:
a single non-linear circuit element, the single non-linear circuit element being a Josephson junction connected between a first circuit node and a second circuit node; and
one or more linear circuit elements, the one or more linear circuit elements comprising a linear inductor connected in parallel with the Josephson junction between the first circuit node and the second circuit node, wherein the linear inductor is a conductive stripline, and the conductive stripline is a superconducting material formed as a straight line; and
a control system configured to operate the superconducting quantum processing circuit.