Josephson polarity and logical inverter gates
AssigneeNorthrop Grumman Systems Corporation
InventorQUENTIN P. HERR
Life of this patent
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Abstract
A Josephson inverter gate circuit provides efficient implementation of polarity or logical inversion while eliminating the need for physically large high-efficiency magnetic transformers in the signal path. The circuit can consist of a half-twisted Josephson transmission line (JTL) or a JTL with an unshunted floating Josephson junction that produces two single flux quantum (SFQ) pulses when triggered by an SFQ input signal, which results in an output SFQ signal of reversed polarity. Implemented as a logical inverter, proper initialization of the circuit is accomplished within the signal inversion stage with flux biasing.
Claims20
A Josephson inverter gate circuit comprising:
- an input to provide an input signal comprising at least one single flux quantum (SFQ) pulse;
- a Josephson transmission line (JTL) comprising at least four Josephson junctions arranged to propagate the input signal to an output, and, additionally, a floating Josephson junction in a central portion of the JTL, by which the JTL is arranged to invert the input signal into an output signal,
- wherein the inverter gate circuit is a reciprocal quantum logic (RQL) inverter capable of inverting the input signal encoded with RQL data encoding having SFQ pulses of either positive or negative polarity.
A method of logically inverting a signal value based on single flux quantum (SFQ) pulse inputs, the method comprising:
- providing a first positive SFQ pulse to an input end of a Josephson transmission line (JTL) to set an input-side Josephson junction in the JTL that is nearer the input end of the JTL than an output end of the JTL to a 2π superconducting phase, the JTL having a floating Josephson junction in a central portion of the JTL between the input and output ends of the JTL;
- before or after providing the first positive SFQ pulse, but before the first positive SFQ pulse can propagate through the central portion of the JTL to the output end of the JTL, injecting one Φ0/2 of current into the floating Josephson junction as an initializing current, such that the first positive SFQ pulse is annihilated by the initializing current and does not propagate through to the output end of the JTL, without affecting the superconducting phase of the input-side Josephson junction;
- and
- providing a negative SFQ pulse to the input end of the JTL to reset the input-side Josephson junction to a 0 superconducting phase, such that the negative SFQ pulse propagates to the output end of the JTL to set to 2π the superconducting phase of an output-side Josephson junction in the JTL that is nearer the output end of the JTL than the input end of the JTL.
A method of logically inverting a signal value based on single flux quantum (SFQ) pulse inputs, the method comprising:
- providing a first negative SFQ pulse to an output end of a Josephson transmission line (JTL) to set an output-side Josephson junction in the JTL that is nearer the output end of the JTL than an input end of the JTL to a 2π superconducting phase, the JTL having a central portion between the input and output ends of the JTL;
- before or after providing the first negative SFQ pulse, but before the first negative SFQ pulse can propagate through the central portion of the JTL to the input end of the JTL, injecting one of:
- one Φ0 of current into a central loop in the central portion of the JTL as an initializing current, such that the first negative SFQ pulse is annihilated by the initializing current and does not propagate through to the input end of the JTL, without affecting the superconducting phase of the output-side Josephson junction, or
- one Φ0/2 of current into a floating Josephson junction in the central portion of the JTL as an initializing current, such that the first negative SFQ pulse is annihilated by the initializing current and does not propagate through to the input end of the JTL, without affecting the superconducting phase of the output-side Josephson junction;
- and
- providing a positive SFQ pulse to the input end of the JTL to set to a 2π superconducting phase an input-side Josephson junction that is nearer the input end of the JTL than the output end of the JTL, such that the positive SFQ pulse propagates to the output end of the JTL to reset to 0 the superconducting phase of the output-side Josephson junction.
Dependencies are inferred from the claim text.