Northrop Grumman Systems Corporation

Microsoft Technology Licensing, LLC

Alexander Louis Braun

Quentin P Herr

Anna Y Herr

Jack R Powell, Iii

Randall M Burnett

Max Earl Nielsen

Haitao O Dai

Kurt Pleim

Harold Clifton Hearne, Iii

Charles Ryan Wallace

Daniel George Dosch

Timothy Chi-Chao Lee

Ryan Edward Clarke

Douglas M Carmean

Adam James Muff

Kenneth S Reneris

Mark Gary Kupferschmidt

Janet Lynn Schneider

Steven Brian Shauck

Brian Lee Koehler

Josh Lance Puckett

David Christopher Harms

Alison Ii

Harold Clifton Hearne

Iii Powell

Jack R Iii Powell

An output-amplifier-based reciprocal quantum logic (RQL) bias-level sensor is used to measure and/or calibrate bias parameters of AC and/or DC bias signals provided to RQL circuitry. The bias signals can include an output amplifier output bias current. The bias-level sensor includes a stack of DC SQUIDs that are supplied their inputs from outputs of respective Josephson transmission lines (JTLs) to which the SQUIDs are transformer-coupled. Staging relative strengths of the bias taps of the JTLs, or the critical currents of the Josephson junctions in the DC SQUIDs, allows an output voltage signal of the bias-level sensor to be indicative of whether a provided bias value is an improvement or optimization of the bias value when varied over a range. The outputs of two such bias-level sensors driven by I and Q clocks can be compared to adjust AC bias amplitudes of the clocks. Relative clock phase can be similarly adjusted.

Squid stack pulse height bias-level sensor for reciprocal quantum logic

Pulse-generator-based reciprocal quantum logic (RQL) bias-level sensors are fabricated on an RQL integrated circuit (IC) to sample AC or DC bias values provided to operational RQL circuitry on the RQL IC. The bias-level sensors include pulse generators having strengthened or weakened bias taps (transformer couplings to RQL AC clock resonators or DC bias lines) as compared to bias taps of Josephson transmission lines in the operational RQL circuitry, or Josephson junctions (JJs) with larger or smaller critical currents as compared to JJs in the operational RQL circuitry. Pulse generators with weakened bias taps or larger JJs can have lower limits of their operational ranges placed near an optimal bias point at the centroid of the operating region of the operational RQL circuitry. The bias-level sensors can be staged by relative strength to indicate whether a provided bias value is an improvement when varied over a range.

Pulse-generator-based bias-level sensors for reciprocal quantum logic

Shift register elements of a phase-mode bit-addressable sensing register sample varied AC or DC bias values provided to operational RQL circuitry on the RQL IC via clock resonators or DC bias lines. The shift register can be constructed of phase-mode D flip-flops and JTLs as data and clock lines. A method of using the sensing register includes shifting in a data bit pattern while a bias parameter (e.g., AC amplitude, DC value, or phase) is set to a nominal value; stopping the logical clock that controls the shifting of values through the sensing register, varying the bias parameter value, inputting one assertion SFQ pulse or reciprocal pulse pair into the logical clock, restoring the bias parameter to the nominal value, restarting the logical clock to shift out an output data bit pattern, and observing the output data bit pattern to determine the effect of the bias parameter value change.

Phase-mode bit-addressable sensing register

One example describes a superconducting XOR-gate system. The system includes a pulse generator configured to generate a decision pulse. The system also includes an input superconducting XOR-2 gate that receives a first superconducting logic input signal and a second superconducting logic input signal and is configured to perform a logic XOR function based on the decision pulse on a given phase of a clock signal to provide an intermediate superconducting logic output signal. The system also includes an output superconducting XOR-2 gate that receives the intermediate superconducting logic output signal and a third superconducting logic input signal and is configured to perform a logic XOR function based on the decision pulse on the given phase of the clock signal to provide a superconducting logic output signal.

Superconducting exclusive-OR (XOR) gate system

Non-destructive read out (NDRO) circuits are provided for use in reciprocal quantum logic (RQL) superconducting systems. Each NDRO circuit includes a 'body' circuit that provides a single or multi-state sub-critical bias current to one or many independent 'tail' circuitries. Each &#x201c;tail&#x201d; has minimal effect on the &#x201c;body&#x201d; thereby preventing any interference or destruction to the state of the &#x201c;body&#x201d; circuitry. The circuits reduce device count and thereby increase circuit density, simplify and reduce the cost of fabrication, and provide functionality not available in existing designs, such as the ability to write a state and read it in the same operation cycle. The NDRO circuits provide more compact unit cells useful in memory or logic arrays, demanding fewer resources with increased functionality. The circuits also provide compact cells for AND, AND-OR, A-NOT-B, inverter, multiplexer, and demultiplexer gates.

Superconducting non-destructive readout circuits

Superconducting circuit with virtual timing elements and related methods are described. A method includes specifying a superconducting circuit portion including a timing path comprising: (1) at least one logic gate to be implemented using Josephson junctions, (2) a first virtual timing element for defining a synchronization point along the timing path, and (3) a second virtual timing element for adding latency to the timing path. The method further includes synthesizing the superconducting circuit portion, where the synthesizing comprises treating the first virtual timing element as a first flip-flop and the second virtual timing element as a second flip-flop, where the first flip-flop is treated as being fixed in relation to the at least one logic gate along the timing path, but the second flip-flop is treated as being movable in relation to the at least one logic gate along the timing path.

Superconducting circuit with virtual timing elements and related methods

A reciprocal quantum logic (RQL) wave-pipeline logic (WPL) inverting gate includes a Josephson junction-based comparator that corrects a design weakness present in other RQL WPL inverting gates that can lead to the propagation of glitches under certain timing conditions. With selective placement of pulse generators at the inputs, the RQL WPL inverting gate can be used to construct A AND (B XOR C) gates, XOR gates, NOT gates, and A-AND-NOT-B gates.

Inverting WPL gates with edge-triggered readout

Superconducting circuits and methods for detecting a rising edge of an input signal are described. An example superconducting circuit includes an input terminal for receiving an input signal comprising both positive pulses and negative pulses. The superconducting circuit further includes a first stage, coupled to the input terminal and a first node, configured to suppress both any backward propagating negative pulses and any forward propagating negative pulses, and allow propagation of any forward propagating positive pulses. The superconducting circuit further includes a second stage, coupled to the first node, configured to store a forward propagating positive pulse and reflect a stored positive pulse back to the first node as a negative pulse such that in response to each rising edge of the input signal a return-to-zero signal comprising both a rising edge and a falling edge is provided as an output at the first node.

Superconducting circuit and method for detecting a rising edge of an input signal

Josephson transmission lines (JTLs) for superconducting devices and related methods are provided. In one example, a device comprising a JTL for propagating quantum pulses in a first direction in response to an application of a clock signal having a plurality of phases is provided. The JTL may include a first inductive element coupled between a first terminal and a second terminal, a first Josephson junction (JJ) coupled between the second terminal and a ground terminal, a second inductive element coupled between the second terminal and a third terminal, and a second JJ coupled between the third terminal and the ground terminal. The second inductive element is configured to form an inductive loop, and the inductive loop may be configured to operate in a mode such that a quantum pulse cannot travel in a second direction opposite from the first direction regardless of a phase of the clock signal.

Josephson transmission line for superconducting devices

A reciprocal quantum logic (RQL) phase-mode flip-flop includes a storage loop and a comparator, each of which includes Josephson junctions (JJs). A data input, provided as a positive or negative single flux quantum (SFQ) pulse, is stored in the storage loop to set the storage loop in a positive or negative state, respectively, effectively biasing an output JJ shared between the storage loop and a comparator. The data input is captured to the output upon the receipt of a logical clock SFQ reciprocal pulse pair to the comparator, when one of the pulses in the pair causes the output JJ to preferentially trigger over an escape junction in the comparator, owing to the output JJ having been biased by current in the storage loop.

RQL phase-mode flip-flop

A reciprocal quantum logic (RQL) phase-mode D flip-flop accepts a data input and a logical clock input. A D flip-flop with an enable input further accepts enable input and further requires that the enable be asserted high to allow the data input to change the output on the logical clock pulse. The flip-flop includes a storage loop and a comparator, each of which includes Josephson junctions (JJs). The storage loop stores the data input, provided as a positive or negative single flux quantum (SFQ) pulse, is stored in the storage loop as positive or negative state, respectively, effectively biasing a JJ shared between the storage loop and the comparator. The data input is captured to the output upon clocking (or enabled clocking), when a clock pulse causes the shared JJ to preferentially trigger over an escape JJ in the comparator, the shared JJ having been biased by storage loop current.

RQL D flip-flops

Superconducting circuits and methods for latching data are described. An example superconducting circuit includes an edge detect circuit configured to receive a logical clock signal and generate a return-to-zero clock signal. The superconducting circuit further includes a first latch configured to receive the logical clock signal and an input data signal, where the first latch is further configured to selectively delay the input data signal to generate a delayed data signal. The superconducting circuit further includes a second latch configured to receive the return-to-zero clock signal and the delayed data signal, where the second latch is further configured to capture a logical high value corresponding to the input data signal in response to a rising edge of the return-to-zero clock signal and capture a low logical value corresponding to the input data signal in response to a falling edge of the return-to-zero clock signal.

Superconducting circuits and methods for latching data

An inverting reciprocal quantum logic (RQL) phase-mode D flip-flop accepts a data input and a logical clock input. The flip-flop includes a stacked Josephson junction and a comparator. The triggering or untriggering of the stacked Josephson junction by positive or negative single flux quantum (SFQ) pulses can switch a direction of DC bias current through a component of the comparator, such as an output Josephson junction, which can then either pass or suppress logical clock SFQ pulses. When so passed, the data input is captured to the output upon clocking the flip-flop via the provision of the logical clock SFQ pulses, e.g., as reciprocal pulse pairs.

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Alexander Louis Braun