The invention provides a method and system for extracting a state machine representation of a digital logic superconductive circuit from an alphanumeric representation of the circuit. The alphanumeric representation typically specifies circuit components including inductive elements, their interconnectivity and input and output nodes. The method according to the invention comprising the steps of simulating the circuit in a suitable software environment utilizing the alphanumeric representation; identifying inductive loops in the circuit; identifying inductive loops in the circuit capable of storing one or more magnetic fluxons and discarding all others; and extracting the state machine representation, using only the inductive loops in the circuit capable of storing magnetic fluxons.

A system for quantum computation and a readout method using the same are provided. In some aspects, the system includes at least one qubit circuit coupled to a resonant cavity, wherein each of the at least one qubit circuit is described by multiple quantum states, and a controller configured to provide microwave irradiation to the resonant cavity such that a quantum state information of the at least one qubit circuit is transferred to a resonant cavity occupation. The system also includes a readout circuit, coupled to the resonant cavity, configured to receive signals corresponding to the resonant cavity occupation, and generate an output indicative of the quantum states of the at least one qubit circuit. Optionally, the system further includes at least one single flux quantum (SFQ) circuit coupled to the readout circuit and configured to receive the output therefrom.

Apparatus and methods enable active compensation for unwanted discrepancies in the superconducting elements of a quantum processor. A qubit may include a primary compound Josephson junction (CJJ) structure, which may include at least a first secondary CJJ structure to enable compensation for Josephson junction asymmetry in the primary CJJ structure. A qubit may include a series LC-circuit coupled in parallel with a first CJJ structure to provide a tunable capacitance. A qubit control system may include means for tuning inductance of a qubit loop, for instance a tunable coupler inductively coupled to the qubit loop and controlled by a programming interface, or a CJJ structure coupled in series with the qubit loop and controlled by a programming interface.

On-chip testing of a superconductive integrated circuit device includes receiving a superconductive circuit design having superconductive logic elements. Further, a first testability characteristic for first test circuitry at a first node within the superconductive circuit design is determined. The first testability characteristic corresponds to one or more of a test generation control level and a test observability control level. An updated superconductive circuit design from the superconductive circuit design is generated based on the first testability characteristic for the first test circuitry. The superconductive circuit design includes the first test circuitry at the first node.

A device includes a logic circuit comprising a clockless single flux quantum logic gate which comprises a plurality of input ports, an output port, an output Josephson junction, and a plurality of dynamic storage loop circuits and isolation buffer circuits. The output Josephson junction is coupled to an output of each dynamic storage loop circuit and configured to drive the output port. Each isolation buffer circuit is coupled to a respective input port, and a respective dynamic storage loop circuit and configured to absorb a circulating current of an antifluxon which is injected into the respective dynamic storage loop circuit to prevent the antifluxon from being output from the respective input port, and to inject a fluxon into the respective dynamic storage loop circuit in response to a single flux quantum pulse applied to the respective input port, and annihilate an antifluxon present in the respective dynamic storage loop circuit.

Apparatus and methods enable active compensation for unwanted discrepancies in the superconducting elements of a quantum processor. A qubit may include a primary compound Josephson junction (CJJ) structure, which may include at least a first secondary CJJ structure to enable compensation for Josephson junction asymmetry in the primary CJJ structure. A qubit may include a series LC-circuit coupled in parallel with a first CJJ structure to provide a tunable capacitance. A qubit control system may include means for tuning inductance of a qubit loop, for instance a tunable coupler inductively coupled to the qubit loop and controlled by a programming interface, or a CJJ structure coupled in series with the qubit loop and controlled by a programming interface.

An on-chip Josephson parametric converter is provided. The on-chip Josephson parametric converter includes a Josephson ring modulator. The on-chip Josephson parametric converter further includes a lossless power divider, coupled to the Josephson ring modulator, having a single input port and two output ports for receiving a pump drive signal via the single input port, splitting the pump drive signal symmetrically into two signals that are equal in amplitude and phase, and outputting each of the two signals from a respective one of the two output ports. The pump drive signal excites a common mode of the on-chip Josephson parametric converter.

An on-chip Josephson parametric converter is provided. The on-chip Josephson parametric converter includes a Josephson ring modulator. The on-chip Josephson parametric converter further includes a lossless power divider, coupled to the Josephson ring modulator, having a single input port and two output ports for receiving a pump drive signal via the single input port, splitting the pump drive signal symmetrically into two signals that are equal in amplitude and phase, and outputting each of the two signals from a respective one of the two output ports. The pump drive signal excites a common mode of the on-chip Josephson parametric converter.

On-chip testing of a superconductive integrated circuit device includes receiving a superconductive circuit design having superconductive logic elements. Further, a first testability characteristic for first test circuitry at a first node within the superconductive circuit design is determined. The first testability characteristic corresponds to one or more of a test generation control level and a test observability control level. An updated superconductive circuit design from the superconductive circuit design is generated based on the first testability characteristic for the first test circuitry. The superconductive circuit design includes the first test circuitry at the first node.