Automatic quantum circuit control skips

1 . A method comprising:

obtaining a sequence of quantum operations, each operation is a tuple of a gate and an ordered sequence of qubits on which the gate operates, the sequence of quantum operations defines a complete order between the quantum operations, the quantum operations comprise at least two computation-uncomputation pairs of operations separated by a sub-sequence of one or more quantum operations, the sequence of quantum operations is part of a quantum circuit control of a quantum circuit;

reducing a number of controls of the quantum circuit by excluding a first computation-uncomputation pair of operations from the quantum circuit control and without excluding a second computation-uncomputation pair of operations from the quantum circuit control, whereby obtaining a reduced control sequence, wherein said reducing the number of controls comprises selecting between reducing the first computation-uncomputation pair and between reducing the second computation-uncomputation pair based on an optimization of a score of the reduced control sequence in comparison to a score of an alternative reduced control sequence in which the second computation-uncomputation pair of operations is reduced and the first computation-uncomputation pair of operations is not reduced, wherein the score is determined based on a score of each operation in a respective quantum circuit control; and

outputting a quantum circuit with the reduced number of controls of the quantum circuit.

2 . The method of claim 1 , wherein the first computation-uncomputation pair and the second computation-uncomputation pair intersect.

3 . The method of claim 2 ,

wherein the first computation-uncomputation pair comprises a first operation and a second operation, the second operation is an inverse operation to the first operation,

wherein the second computation-uncomputation pair comprises the first operation and a third operation, the third operation is an inverse operation to the first operation,

wherein the sub-sequence of the first computation-uncomputation pair includes the third operation or the sub-sequence of the second computation-uncomputation pair includes the second operation, whereby due to exclusion of the first computation-uncomputation pair, the second computation-uncomputation pair cannot be excluded.

4 . The method of claim 2 ,

wherein the first computation-uncomputation pair comprises a first operation and a second operation, the second operation is an inverse operation to the first operation,

wherein the second computation-uncomputation pair comprises a third operation and a fourth operation, the fourth operation is an inverse operation to the third operation,

wherein the sub-sequence of the first computation-uncomputation pair includes the third operation or the fourth operation,

wherein the sub-sequence of the second computation-uncomputation pair includes the first operation or the second operation.

5 . The method of claim 1 , wherein the sequence of quantum operations comprises n quantum operations denoted as o 1 , o 2 , . . . , o n , wherein said reducing comprises computing S 1,n , wherein S i,j is a score indicating maximal utility from skipping operations in the control sequence defined by a sub-sequence of o i , o i+1 , . . . , o j , wherein S 1,n is computed based on a summation of S(o l ) for each skipped operation or in the control sequence, wherein S(o l ) is a score defined for skipping the operation o l in the control sequence.

6 . The method of claim 5 , wherein S i,j is computed according to one of the following:

S

i

,

j

=

max

⁢

{

S

i

+

1

,

j

,

,

S

⁡

(

o

i

)

+

max

k

∈

[

i

+

1

,

j

]

⁢

and

⁢

o

k

=

o

i

-

1

S

i

+

1

,

k

-

1

+

S

k

+

1

,

j

,

}

,

S

i

,

j

=

max

⁢

{

S

i

,

j

-

1

,

,

S

⁡

(

o

j

)

+

max

k

∈

[

i

,

j

-

1

]

⁢

and

⁢

o

k

=

o

i

-

1

S

i

,

k

-

1

+

S

k

,

j

-

1

,

}

.

7 . The method of claim 5 , wherein the S(o l ) score is different for different quantum operations that is defined based on a reduction in quantum resources when skipping operation o l from the control of the quantum circuit.

8 . The method of claim 1 , wherein said obtaining the sequence of quantum operations comprises: selecting the sequence of quantum operations based on partial order defined by a quantum program defining the quantum circuit, wherein the quantum program defines a set of alternative sequences in view of commuting quantum operations.

9 . The method of claim 8 , wherein said selecting comprises:

obtaining a circuit Directed Acyclic Graph (DAG) based on the quantum program, wherein each node in the circuit-DAG represents a quantum operation, each directed edge in the circuit-DAG from a first node to a second node represents that the operation represented by the second node immediately follows the operation represented by the first node in the quantum circuit;

constructing, based on the circuit-DAG, a commutation-DAG of the quantum circuit, the commutation-DAG represents partial order between quantum operations of the quantum circuit in view of commutation property of quantum operations pairs;

selecting a sequence of the quantum operations based on the partial order defined by the commutation-DAG.

10 . The method of claim 9 , wherein said selecting is performed using a solver that is configured to solve a selection problem from potential alternative sequences defined by the commutation-DAG, wherein the solver is configured to select the sequence so as to optimize a target function that is based on a score of the selected sequence, the score of the selected sequence is defined based on a score of the potential alternative sequences, the score is determined based on a score of each operation skipped in a respective quantum circuit control in a circuit that is defined based on the potential alternative sequences.

11 . The method of claim 10 , wherein the solver is at least one of a Constraint Satisfaction Problem (CSP) solver and an integer programming problem solver.

12 . The method of claim 9 , wherein said constructing comprises generating a maximal edges circuit-DAG based on the circuit-DAG, the maximal edges circuit-DAG is a closure of the circuit-DAG, wherein the commutation-DAG is constructed by removing edges from the maximal edges circuit-DAG based on commutation property of operations of nodes connected by the edges.

13 . The method of claim 1 further comprises reducing a set of basis gates in the sequence.

14 . A computerized apparatus having a processor, the processor being adapted to perform the steps of:

obtaining a sequence of quantum operations, each operation is a tuple of a gate and an ordered sequence of qubits on which the gate operates, the sequence of quantum operations defines a complete order between the quantum operations, the quantum operations comprise at least two computation-uncomputation pairs of operations separated by a sub-sequence of one or more quantum operations, the sequence of quantum operations is part of a quantum circuit control of a quantum circuit;

reducing a number of controls of the quantum circuit by excluding a first computation-uncomputation pair of operations from the quantum circuit control and without excluding a second computation-uncomputation pair of operations from the quantum circuit control, whereby obtaining a reduced control sequence, wherein said reducing the number of controls comprises selecting between reducing the first computation-uncomputation pair and between reducing the second computation-uncomputation pair based on an optimization of a score of the reduced control sequence in comparison to a score of an alternative reduced control sequence in which the second computation-uncomputation pair of operations is reduced and the first computation-uncomputation pair of operations is not reduced, wherein the score is determined based on a score of each operation in a respective quantum circuit control; and

outputting a quantum circuit with the reduced number of controls of the quantum circuit.

15 . A computer program product comprising a non-transitory computer readable storage medium retaining program instructions, which program instructions when read by a processor, cause the processor to perform a method comprising:

obtaining a sequence of quantum operations, each operation is a tuple of a gate and an ordered sequence of qubits on which the gate operates, the sequence of quantum operations defines a complete order between the quantum operations, the quantum operations comprise at least two computation-uncomputation pairs of operations separated by a sub-sequence of one or more quantum operations, the sequence of quantum operations is part of a quantum circuit control of a quantum circuit;

reducing a number of controls of the quantum circuit by excluding a first computation-uncomputation pair of operations from the quantum circuit control and without excluding a second computation-uncomputation pair of operations from the quantum circuit control, whereby obtaining a reduced control sequence, wherein said reducing the number of controls comprises selecting between reducing the first computation-uncomputation pair and between reducing the second computation-uncomputation pair based on an optimization of a score of the reduced control sequence in comparison to a score of an alternative reduced control sequence in which the second computation-uncomputation pair of operations is reduced and the first computation-uncomputation pair of operations is not reduced, wherein the score is determined based on a score of each operation in a respective quantum circuit control; and

outputting a quantum circuit with the reduced number of controls of the quantum circuit.