Single flux quantum circuitry for quantized flux bias control

Patent metadata

Field	Value
Publication number	US-12150389-B2
Application number	US-202318128447-A
Country	US
Kind code	B2
Filing date	Mar 30, 2023
Priority date	Mar 30, 2023
Publication date	Nov 19, 2024
Grant date	Nov 19, 2024

Abstract

A system comprises a superconducting quantizing inductor and superconducting control circuitry, which is coupled to the superconducting quantizing inductor to form a superconducting loop, and which is configured to selectively inject a quantized amount of positive or negative current into the superconducting loop to generate a quantized circulating current in the superconducting loop. The quantized circulating current comprises a time-varying or static circulating current. The superconducting control circuitry comprises first and second current generator circuits which comprise a first and second plurality of Josephson junctions, respectively, which are configured to inject quantized amounts of positive current and negative current into the superconducting loop in response to single flux quantum pulses. The first and second current generator circuits comprise respective first and second current distribution networks that are configured to distribute circulating current in the superconducting loop to the respective Josephson junctions without causing switching of the Josephson junctions.

First claim

What is claimed is:

1. A system, comprising:
a superconducting inductor comprising a quantizing inductance; and
superconducting control circuitry which is coupled to the superconducting inductor to form a superconducting loop, and which is configured to selectively inject a quantized amount of positive current or negative current into the superconducting loop to generate a quantized circulating current in the superconducting loop, wherein the quantized circulating current comprises one of a time-varying circulating current and a static circulating current;
wherein the superconducting control circuitry comprises:
a first current generator circuit comprising a first plurality of Josephson junctions and a first current distribution network, wherein the first plurality of Josephson junctions are configured to inject a quantized amount of positive current into the superconducting loop in response to each single flux quantum pulse applied to the first current generator circuit; and
a second current generator circuit comprising a second plurality of Josephson junctions and a second current distribution network, wherein the second plurality of Josephson junctions are configured to inject a quantized amount of negative current into the superconducting loop in response to each single flux quantum pulse applied to the second current generator circuit;
wherein the first current distribution network is configured to distribute a quantized circulating negative current in the superconducting loop to the first plurality of Josephson junctions to sink the quantized circulating negative current to a ground node through the first plurality of Josephson junctions without causing a switching of any of the first plurality of Josephson junctions; and
wherein the second current distribution network is configured to distribute a quantized circulating positive current in the superconducting loop to the second plurality of Josephson junctions to sink the quantized circulating positive current to the ground node through the second plurality of Josephson junctions without causing a switching of any of the second plurality of Josephson junctions.

2. The system of claim 1 , wherein:
the first current generator circuit comprises a first feeding Josephson transmission line circuit coupled to a first terminal of the superconducting inductor, wherein the first feeding Josephson transmission line circuit comprises a first Josephson transmission line comprising the first plurality of Josephson junctions, and wherein the first current distribution network is coupled to and between the first Josephson transmission line and the first terminal of the superconducting inductor; and
the second current generator circuit comprises a second feeding Josephson transmission line circuit coupled to a second terminal of the superconducting inductor, wherein the second feeding Josephson transmission line circuit comprises a second Josephson transmission line comprising the second plurality of Josephson junctions, and wherein the second current distribution network is coupled to and between the second Josephson transmission line and the second terminal of the superconducting inductor.

3. The system of claim 2 , wherein the first feeding Josephson transmission line circuit, the second feeding Josephson transmission line circuit, and the superconducting inductor collectively form the superconducting loop.

4. The system of claim 2 , wherein the first Josephson transmission line and the second Josephson transmission line are non-amplifying Josephson transmission lines.

5. The system of claim 2 , wherein:
the first current distribution network comprises a first balanced inductor H-tree circuit; and
the second current distribution network comprises a second balanced inductor H-tree circuit.

6. The system of claim 2 , further comprising:
a first bias current generator configured to generate a first static bias current; and
a second bias current generator configured to generate a second static bias current;
wherein the first current distribution network is coupled to the first bias current generator and configured to distribute the first static bias current to each Josephson junction of the first plurality of Josephson junctions; and
wherein the second current distribution network is coupled to the second bias current generator and configured to distribute the second static bias current to each Josephson junction of the second plurality of Josephson junctions.

7. The system of claim 1 , wherein:
the first current generator circuit comprises a first balanced tree circuit structure which comprises a first port, a second port, a first single flux quantum splitter tree, and a first Josephson junction stage which comprises the first plurality of Josephson junctions and the first current distribution network;
the second current generator circuit comprises a second balanced tree circuit structure which comprises a first port, a second port, a second single flux quantum splitter tree, and a second Josephson junction stage which comprises the second plurality of Josephson junctions and the second current distribution network;
a first terminal of the superconducting inductor is coupled to the second port of the first balanced tree circuit structure;
a second terminal of the superconducting inductor is coupled to the second port of the second balanced tree circuit structure; and
the first Josephson junction stage, the second Josephson junction stage, and the superconducting inductor collectively form the superconducting loop.

8. The system of claim 7 , wherein:
the first single flux quantum splitter tree is configured to distribute a single flux quantum pulse, which is applied to the first port of the first balanced tree circuit structure, to each Josephson junction of the first plurality of Josephson junctions of the first Josephson junction stage, and cause each Josephson junction to generate a quantized amount of positive current that is injected into the superconducting loop; and
the second single flux quantum splitter tree is configured to distribute a single flux quantum pulse, which is applied to the first port of the second balanced tree circuit structure, to each Josephson junction of the second plurality of Josephson junctions of the second Josephson junction stage, and cause each Josephson junction to generate a quantized amount of negative current that is injected into the superconducting loop.

9. The system of claim 8 , wherein the Josephson junctions of the first plurality of Josephson junctions and the second plurality of Josephson junctions have a same critical current.

10. The system of claim 1 , wherein the superconducting control circuitry further comprises:
a pulse generator circuit configured to generate successive single flux quantum pulses in response to an oscillating control signal which drives the pulse generator circuit; and
a switch circuit configured to selectively apply one or more successive single flux quantum pulses to one of: an input port of the first current generator circuit to cause the first current generator circuit to inject a quantized amount of positive current into the superconducting loop; and an input port of the second current generator circuit to cause the second current generator circuit to inject a quantized amount of negative current into the superconducting loop.

11. The system of claim 10 , wherein the switch circuit comprises a single flux quantum single pole, double throw switch which comprises an input port to receive the one or more successive single flux quantum pulses, a first output port to selectively output the one or more successive single flux quantum pulses to the input port of the

Assignees

• IBM

Inventors

• Beck Matthew
• Robertazzi Raphael Peter
• Bulzacchelli John Francis

Classifications

• H03K3/38

  by the use, as active elements, of superconductive devices · CPC title

• H03K19/195

  using superconductive devices · CPC title

• H10N60/805

  for Josephson-effect devices · CPC title

• G06N10/40

  Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control · CPC title

• G06N10/00

  Quantum computing, i.e. information processing based on quantum-mechanical phenomena · CPC title