Measurement based uncomputation for quantum circuit optimization
AssigneeGoogle Inc.
InventorCraig Gidney
Life of this patent
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Abstract
Methods and apparatus for optimizing a quantum circuit. In one aspect, a method includes identifying one or more sequences of operations in the quantum circuit that un-compute respective qubits on which the quantum circuit operates; generating an adjusted quantum circuit, comprising, for each identified sequence of operations in the quantum circuit, replacing the sequence of operations with an X basis measurement and a classically-controlled phase correction operation, wherein a result of the X basis measurement acts as a control for the classically-controlled correction phase operation; and executing the adjusted quantum circuit.
Claims20
A method for uncomputing a first table lookup operation, the method comprising:
- identifying, from an address register of qubits, a set of qubit states that require an amplitude negation to complete an uncomputation of the first table lookup operation, wherein qubits in the address register represent respective bit values;
- computing i) a first qubit in the address register and ii) a second qubit, wherein the first qubit represents a least significant bit of the respective bit values and the second qubit comprises an ancilla qubit prepared in a 1 state, the computing comprising
- applying a first CNOT operation to the first qubit and the second qubit, wherein the first qubit acts as a control for the first CNOT operation, and
- applying a first Hadamard gate to the first qubit and a second Hadamard gate to the second qubit;
- performing a classically controlled phase correction operation based on the identified set of qubit states, comprising applying a second table lookup operation from a fixup table onto the first qubit and second qubit to negate amplitudes of the states in the identified set of qubit states;
- and
- uncomputing the first qubit and the second qubit.
The method of claim, 1, wherein uncomputing the first qubit and the second qubit comprises:
- applying a third Hadamard gate to the first qubit and a fourth Hadamard gate to the second qubit;
- and
- applying a second CNOT operation to the first qubit and the second qubit, wherein the first qubit acts as a control for the second CNOT operation.
An apparatus comprising:
- one or more classical processors;
- and
- quantum computing hardware in data communication with the one or more classical processors,
- wherein the one or more classical processors comprise one or more storage devices storing instructions that are operable, when executed by the one or more classical processors, to cause the one or more classical processors to perform operations comprising:
- identifying, from an address register of qubits, a set of qubit states that require an amplitude negation to complete an uncomputation of a first table lookup operation, wherein qubits in the address register represent respective bit values;
- computing i) a first qubit in the address register and ii) a second qubit, wherein the first qubit represents a least significant bit of the respective bit values and the second qubit comprises an ancilla qubit prepared in a 1 state, the computing comprising
- applying a first CNOT operation to the first qubit and the second qubit, wherein the first qubit acts as a control for the first CNOT operation, and
- applying a first Hadamard gate to the first qubit and a second Hadamard gate to the second qubit;
- performing a classically controlled phase correction operation based on the identified set of qubit states, comprising applying a second table lookup operation from a fixup table onto the first qubit and second qubit to negate amplitudes of the states in the identified set of qubit states;
- and
- uncomputing the first qubit and the second qubit.
The apparatus of claim, 11, wherein uncomputing the first qubit and the second qubit comprises:
- applying a third Hadamard gate to the first qubit and a fourth Hadamard gate to the second qubit;
- and
- applying a second CNOT operation to the first qubit and the second qubit, wherein the first qubit acts as a control for the second CNOT operation.
Dependencies are inferred from the claim text.