Qubit state monitoring in quantum computers utilizing radio frequency superconducting quantum interference devices with classical computer readout and processing
The technology described herein is directed towards real-time monitoring of qubit states in quantum computers using a system based on rf-SQUIDs (radio-frequency superconducting quantum interference devices) and a direct current signal that is sourced to a superconducting quantum circuit wire, and measured by, a classical computing device. In one implementation, the rf-SQUIDs are positioned at strategic locations, between superconducting quantum circuit wires, in a quantum computer, such as before and after attenuators, and before parametric amplifiers. The direct current control signal facilitates the detection of magnetic flux and inductance without adding load or noise to the superconducting quantum circuit wires, which enhances the detection of qubit state changes. The monitoring and detection system dynamically and precisely monitors qubit state changes and provides real-time feedback to the quantum processing unit to adjust the qubit states, and thereby maintain the integrity of quantum computations.
1 . A system, comprising:
a group of radio frequency-superconducting quantum interference devices (rf-SQUIDs) positioned between a first superconducting quantum circuit wire corresponding to a send path to a quantum circuit, and a second superconducting quantum circuit wire corresponding to a return path from the quantum circuit,
wherein the group of rf-SQUIDs is configured to monitor magnetic flux corresponding to a state of a qubit of the quantum circuit,
wherein the group of rf-SQUIDs is configured to monitor an inductance corresponding to the state of the qubit of the quantum circuit; and
a computing device coupled to the first superconducting quantum circuit wire and the second superconducting quantum circuit wire, the computing device configured to source direct current to the first superconducting quantum circuit wire, and to measure the direct current to determine whether the direct current is varied by a magnetic flux change that results from a state transition of the qubit.
2 . The system of claim 1 , wherein the computing device determines that the direct current was varied based on a state transition of the qubit, and wherein the computing device communicates feedback data corresponding to the state transition of the qubit to a quantum processor for state adjustment of the qubit.
3 . The system of claim 1 , wherein the computing device comprises a source measure unit configured to source the direct current and to measure the direct current.
4 . The system of claim 3 , wherein the source measure unit is integrated into a peripheral component interconnect express card that is incorporated into the computing device.
5 . The system of claim 1 , wherein the direct current is first direct current sourced at a first level, and wherein the computing device adjusts the first direct current at the first level to a second direct current at a second level a sourced from the computing device based on a measurement of the first direct current at the first level.
6 . The system of claim 1 , wherein the group of rf-SQUIDs comprises at least four rf-SQUIDs.
7 . The system of claim 1 , wherein the group of rf-SQUIDs comprises an rf-SQUID positioned proximate to a coupler of a quantum computer associated with the quantum circuit.
8 . The system of claim 1 , wherein the group of rf-SQUIDs comprises an rf-SQUID positioned proximate to a splitter section of a quantum computer associated with the quantum circuit.
9 . The system of claim 1 , wherein the group of rf-SQUIDs comprises an rf-SQUID positioned proximate to a combiner section of a quantum computer associated with the quantum circuit.
10 . The system of claim 1 , wherein an attenuator is coupled to the first superconducting quantum circuit wire, and wherein the group of rf-SQUIDs comprises an rf-SQUID positioned before the attenuator with respect to a direction of the send path.
11 . The system of claim 1 , wherein an attenuator is coupled to the first superconducting quantum circuit wire, and wherein the group of rf-SQUIDs comprises an rf-SQUID positioned after the attenuator with respect to a direction of the send path.
12 . The system of claim 1 , wherein a traveling wave parametric amplifier is coupled to the first superconducting quantum circuit wire, and wherein the group of rf-SQUIDs comprises an rf-SQUID positioned before the traveling wave parametric amplifier with respect to a direction of the send path.
13 . A method, comprising:
sending, by a system comprising at least one processor, a direct current control signal on a first superconducting quantum circuit wire to a quantum circuit associated with a qubit, wherein the first superconducting quantum circuit wire is proximate to a group of radio frequency-superconducting quantum interference devices (rf-SQUIDs) to monitor qubit states; and
evaluating, by the system, the direct current control signal to determine whether at least one of the rf-SQUIDS varies the direct current control signal based on a magnetic flux change that results from a state transition of the qubit.
14 . The method of claim 13 , further comprising determining, by the system based on the evaluating of the direct current control signal, a state transition of the qubit, and communicating, by the system, information corresponding to the state transition of the qubit, to a quantum processor associated with the quantum circuit for adjustment of a state of the qubit.
15 . The method of claim 13 , further comprising adjusting, by the system, a current level of the direct current control signal to change a monitoring parameter of the group of rf-SQUIDs.
16 . The method of claim 13 , further comprising adjusting, by the system, a current level of the direct current control signal to change an inductance of the group of rf-SQUIDs.
17 . The method of claim 13 , further comprising adjusting, by the system, a current level of the direct current control signal to change relative phase shift response data of the group of rf-SQUIDs.
18 . A non-transitory machine-readable medium, comprising executable instructions that, when executed by at least one processor, facilitate performance of operations, the operations comprising:
outputting a direct current control signal on a first superconducting quantum circuit wire corresponding to a send path to a quantum circuit associated with a qubit, the first superconducting quantum circuit wire coupled to a group of radio frequency-superconducting quantum interference devices (rf-SQUIDs), the group of rf-SQUIDs being positioned between the first superconducting quantum circuit wire and a second superconducting quantum circuit wire corresponding to a return path from the quantum circuit;
measuring the direct current control signal; and
determining, based on a result of the measuring of the direct current control signal, a state change of the qubit.
19 . The non-transitory machine-readable medium of claim 18 , wherein the operations further comprise communicating information corresponding to the state change to a quantum processor associated with the quantum circuit for adjustment of a state of the qubit.
20 . The non-transitory machine-readable medium of claim 18 , wherein the operations further comprise adjusting the current level of the direct current control signal from a first current level to a second current level based on the result of the measuring of the direct current control signal.