Systems and methods for superconducting flux qubit readout

A method of reading out a state of a superconducting flux qubit, the method comprising:

• coupling a magnetic flux representative of the state of the superconducting flux qubit from the superconducting flux qubit to a DC-SQUID, wherein the DC-SQUID is electrically coupled in parallel with a primary inductor with respect to a signal input line;
• applying a time-varying drive current in the signal input line by a signal input source such that a fraction of the time-varying drive current is routed through the primary inductor;
• inductively coupling the primary inductor to a secondary inductor, wherein the secondary inductor is electrically coupled in series with a signal output line, such that a time-varying output signal is transmitted through the signal output line;
• and
• determining a characteristic of the time-varying output signal indicative of the state of the superconducting flux qubit.

A method of reading out a state of each superconducting flux qubit in a plurality of superconducting flux qubits, the method comprising:

• latching the state of each superconducting flux qubit using a respective latching qubit to define a plurality of latched states;
• coupling the latched states to a routing system comprising a plurality of additional latching qubits;
• coupling the latched state corresponding to a first superconducting flux qubit from the routing system to a DC-SQUID, wherein the DC-SQUID is electrically coupled in parallel with a primary inductor with respect to a signal input line;
• using a signal input source to apply a time-varying drive current in the signal input line such that a fraction of the time-varying drive current is routed through the primary inductor;
• inductively coupling the primary inductor to a secondary inductor, wherein the secondary inductor is electrically coupled in series with a signal output line, such that a time-varying output signal is transmitted through the signal output line;
• determining a characteristic of the time-varying output signal to determine the state of the first superconducting flux qubit;
• operating the routing system to couple the latched state corresponding to a second superconducting flux qubit from the routing system to the DC-SQUID;
• coupling the latched state corresponding to the second superconducting flux qubit from the routing system to the DC-SQUID;
• using the signal input source to apply time-varying drive current in the signal input line such that a fraction of the time-varying drive current is routed through the primary inductor;
• inductively coupling the primary inductor to the secondary inductor such that a time-varying output signal is transmitted through the signal output line;
• and
• determining a characteristic of the time-varying output signal to determine the state of the second superconducting flux qubit.