Read out of quantum states of microwave frequency qubits with optical frequency photons

A method of reading N qubits respectively coupled to N microwave resonators, the method comprising:

• inputting N microwave input readout signals at N microwave resonator frequencies to the N microwave resonators respectively coupling the N qubits, wherein N is an integer, wherein one of the N microwave resonator frequencies individually corresponds to one of the N microwave resonators;
• outputting N microwave output readout signals from the N microwave resonators to N microwave to optical converters, the N microwave output readout signals individually including a qubit state of the N qubits, wherein the N microwave to optical converters are configured to convert the N microwave output readout signals to N optical signals, wherein one of the N microwave output readout signals individually corresponds to one of the N qubits, wherein a photon detector is coupled to an output optical waveguide of the N microwave to optical converters, the N microwave to optical converters being separate devices from the photon detector;
• in response to any of the N optical signals being output by the N microwave to optical converters, determining that corresponding ones of the N qubits are in a predefined qubit state by the photon detector detecting the optical signal from the microwave to optical converter;
• and
• in response to no optical signal being output by any of the N microwave to optical converters, determining that corresponding ones of the N qubits are not in the predefined qubit state by the photon detector failing to detect the optical signal from the microwave to optical converter.

A system for reading N qubits, the system comprising:

• N microwave resonators coupled to the N qubits, the N microwave resonators configured to receive N microwave input readout signals at N microwave resonator frequencies and output N microwave output readout signals, wherein N is an integer;
• and
• N microwave to optical converters configured to receive the N microwave output readout signals from the N microwave resonators, the N microwave output readout signals individually including a qubit state of the N qubits, wherein the N microwave to optical converters are configured to convert the N microwave output readout signals to N optical signals, wherein one of the N microwave output readout signals individually corresponds to one of the N qubits, wherein a photon detector is coupled to an output optical waveguide of the N microwave to optical converters, the N microwave to optical converters being separate devices from the photon detector, wherein ones of the N qubits are respectively defined to be in a predefined qubit state when corresponding ones of the N optical signals are detected by the photon detector as being output by corresponding ones of the N microwave to optical converters, wherein corresponding ones of the N qubits are defined to not be in the predefined qubit state when no corresponding ones of the N optical signals are output by corresponding ones of the N microwave to optical converters.

A readout system for reading one or more qubits, the readout system comprising:

• one or more microwave waveguides;
• one or more optical waveguides;
• and
• one or more microwave to optical converters configured to receive one or more microwave readout signals corresponding to the one or more qubits via the one or more waveguides, wherein a photon detector is coupled to an output optical waveguide of the microwave to optical converter, the microwave to optical converter being a separate device from the photon detector, wherein the one or more microwave to optical converters are configured to output one or more optical signals for the one or more qubits being in a predefined qubit state via the one or more optical waveguides, wherein the one or more microwave to optical converters are configured to output no optical signals for the one or more qubits not being in the predefined qubit state.