Method and system that implement a V-gate quantum circuit

Patent metadata

Field	Value
Publication number	US-9633313-B2
Application number	US-201313948171-A
Country	US
Kind code	B2
Filing date	Jul 23, 2013
Priority date	Mar 14, 2013
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

The current application is directed to methods and quantum circuits that prepare qubits in specified non-stabilizer quantum states that can, in turn, be used for a variety of different purposes, including in a quantum-circuit implementation of an arbitrary single-qubit unitary quantum gate that imparts a specified, arbitrary rotation to the state-vector representation of the state of an input qubit. In certain implementations, the methods and systems consume multiple magic-state qubits in order to carry out probabilistic rotation operators to prepare qubits with state vectors having specified rotation angles with respect to a rotation axis. These qubits are used as resources input to various quantum circuits, including the quantum-circuit implementation of an arbitrary single-qubit unitary quantum gate, including a V gate.

First claim

The invention claimed is:

1. A V-gate quantum circuit device, comprising:
a control-qubit-generation quantum-circuit subsystem that generates a first rotation control qubit;
a first rotation quantum-circuit subsystem that performs a first rotation on a subject qubit input to the first rotation quantum-circuit subsystem along with the rotation control qubit; and
a second rotation quantum-circuit subsystem that performs a second rotation on the subject qubit input to the second rotation quantum-circuit subsystem along with a control qubit, wherein the control-qubit-generation quantum-circuit subsystem comprises:
one or more stages, each stage i including
a stage i control-qubit input,
a stage i subject-qubit input,
a stage i measurement output that outputs a physical measurement of an input control qubit following at least one internal two-qubit controlled-gate operation, and
a stage i subject-qubit output that outputs the subject qubit following the at least one internal two-qubit controlled-gate operation; and

a controller that monitors the measurements output from the measurement output of successive stages of the control-qubit-generation quantum-circuit subsystem to determine a number of stages to apply to the subject qubit in order to rotate the state vector of the subject qubit to a specified rotation angle within the plane, wherein each qubit is a physical qubit.

2. The V-gate quantum circuit device of claim 1 , wherein the subject qubit input and control qubit input to the first stage of the control-qubit-generation quantum-circuit subsystem both have a state |H 0 =cos θ 0 |0 +sin θ 0 |1 where the rotation angle

θ
0

=

π
8

.

3. The V-gate quantum circuit device of claim 1 , wherein each stage of the control-qubit-generation quantum-circuit subsystem further comprises:
a controlled-NOT gate; and
a measurement gate that physically measures the state of the control qubit following the at least one internal two-qubit controlled-gate operation and outputs an indication m of the measured state to the measurement output.

4. The V-gate quantum circuit device of claim 3 , wherein, when the measurement gate returns an indication m=0 indicating that the control qubit is measured to be in a state |0 , the subject qubit is in a state |H i+1 , with the state-vector representing the state |H i+1 having a rotation angle θ i+1 ; and
wherein, when the measurement gate returns an indication m=1 indicating that the control qubit is measured to be in a state |1 , the subject qubit is in a state |H i−1 , with the state-vector representing the state |H i−1 ) having a rotation angle θ i−1 ,
wherein θ j represents the rotation angle produced from a successful application of stage i−1 .

5. The V-gate quantum circuit device of claim 4 , wherein the measurement gate returns an indication m=0 with a probability p greater than or equal to 0.75 and returns an indication m=1 with a probability p less than or equal to 0.25 at each stage.

6. The V-gate quantum circuit device of claim 1 , wherein the subject qubit output from a stage, subject-qubit output of the control-qubit-generation is input to a stage i+1 subject-qubit input.

7. The V-gate quantum circuit device of claim 6 , wherein, after application of a next stage i of the quantum-circuit subsystem to a subject qubit input to the stage i in state |H i , when the measurement gate of the stage returns an indication m=0 indicating that the control qubit is measured to be in a state |0 , the subject qubit is in state |H i+1 and has a rotation angle θ i+1 k characteristic of the subject qubit input to the first stage of the quantum-circuit subsystem, k, and of the stage i.

8. The V-gate quantum circuit device of claim 7 , wherein the controller:
initially determines a number of stages j to apply to the subject qubit in order to rotate the state vector of the subject qubit to a specified rotation angle; and
while j is greater than 0,
applies a next stage to the subject qubit,
when the measurement value m output after applying the next stage is 0, decrements j, and
when the measurement value m output after applying the next stage is 1, increments j.

9. The V-gate quantum circuit device of claim 1 , wherein the control-qubit-generation quantum-circuit subsystem generates a control qubit in state |H 2 .

10. The V-gate quantum circuit device of claim 1 , wherein the first rotation quantum-circuit subsystem and the second rotation quantum-circuit subsystem each further comprises:
a controlled-NOT; and
a measurement gate.

11. The V-gate quantum circuit device of claim 10 further comprising one of an HS † gate and an HSHX gate that operates on the control qubit in state |H 2 =cos θ 2 |0 +sin θ 2 |1 to prepare a first-rotation-quantum-circuit subsystem control qubit, wherein θ 2 represents the rotation angle produced from a successful application of stage 1 .

12. The V-gate quantum circuit device of claim 11 , wherein the first rotation quantum-circuit subsystem rotates the subject qubit by

-

π
2

+

2
⁢

⁢

θ
2

radians; and
wherein the second rotation quantum-circuit subsystem rotates the subject qubit by

-

π
4

radians.

13. The V-gate quantum circuit device of claim 10 ,
wherein the first rotation quantum-circuit subsystem rotates the subject qubit by 2θ 2 radians, θ 2 representing the rotation angle produced from a successful application of stage 1 ;
wherein the second rotation quantum-circuit subsystem rotates the subject qubit by π radians; and
further comprising a third rotation quantum-circuit subsystem that rotates the subject qubit by

π
4

radians.

14. A method for carrying out a V-gate operation on a subject qubit implemented in hardware, the method comprising:
generating a control qubit using at least one quantum circuit subsystem;
applying a quantum gate to the control qubit to prepare a first rotation control qubit;
performing a first rotation on the subject qubit using the first rotation control qubit;
performing a second rotation on the subject qubit using a second rotation control qubit;
performing a physical measurement of an input control qubit following at least one of the rotations; and
monitoring, using a controller, the physical measurements to determine a number of stages to apply to the subject qubit in order to rotate the state vector of the subject qubit to a specified rotation angle within the plane, wherein each qubit is a physical qubit and the generated control qubit is in state |H 2 =cos θ 2 |0 +sin θ 2 |1 and

Assignees

• Microsoft Corp
• Microsoft Technology Licensing Llc

Inventors

• Svore Krysta
• Duclos-Cianci Guillaume

Classifications

• G06N99/002 Primary

  Physics · mapped topic

• B82Y10/00

  Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic · 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

• G06N10/20 Primary

  Models of quantum computing, e.g. quantum circuits or universal quantum computers · CPC title