Simulating quantum circuits

Abstract

A computer implemented method includes receiving a digital description of a quantum circuit, partitioning the digital description of the quantum circuit into a plurality of quantum sub-circuits wherein each quantum sub-circuit of the plurality of quantum sub-circuits comprises one or more quantum gates, determining sub-circuit dependencies for the plurality of quantum sub-circuits, simulating the plurality of quantum sub-circuits according to the sub-circuit dependencies to produce simulation results for each quantum sub-circuit of the plurality of quantum sub-circuits, wherein a first and a second quantum sub-circuit of the plurality of quantum sub-circuits each contain one or more gates that are applied to a common qubit, and wherein the first and the second quantum sub-circuit are simulated independently using an entangled tensor index. A corresponding computer system and computer program product are also disclosed herein.

What is claimed is: 
     
         1 . A method, executed by one or more processors, for simulating a quantum circuit comprising a plurality of quantum gates, the method comprising:
 receiving a digital description of the quantum circuit comprising a plurality of stages;   creating a sub-circuit for each initial stage qubit to produce a plurality of sub-circuits;   iteratively adding connected non-bridging gates from one or more subsequent stages of the plurality of stages to the plurality of sub-circuits until no more connected non-bridging gates are available;   selecting a bridging gate that is connected to two or more sub-circuits of the plurality of sub-circuits;   determining whether to entangle the two or more sub-circuits; and   adding the bridging gate to only one of the two or more sub-circuits responsive to determining to entangle the two or more sub-circuits.   
     
     
         2 . The method of  claim 1 , further comprising creating a new sub-circuit and assigning the bridging gate to the new sub-circuit responsive to determining to not entangle the two or more sub-circuits. 
     
     
         3 . The method of  claim 1 , further comprising adding the new sub-circuit to the plurality of sub-circuits. 
     
     
         4 . The method of  claim 1 , further comprising closing the two or more sub-circuits. 
     
     
         5 . The method of  claim 1 , further comprising determining whether all gates have been assigned to a sub-circuit. 
     
     
         6 . The method of  claim 1 , further comprising determining sub-circuit dependencies for the plurality of sub-circuits. 
     
     
         7 . The method of  claim 6 , further comprising executing the quantum circuit according to the sub-circuit dependencies. 
     
     
         8 . A computer program product comprising one or more computer readable storage media and program instructions stored on the one or more computer readable storage media, the program instructions executable to:
 receive digital description of the quantum circuit comprising a plurality of stages;   create a sub-circuit for each initial stage qubit to produce a plurality of sub-circuits;   iteratively add connected non-bridging gates from one or more subsequent stages of the plurality of stages to the plurality of sub-circuits until no more connected non-bridging gates are available;   select a bridging gate that is connected to two or more sub-circuits of the plurality of sub-circuits;   determine whether to entangle the two or more sub-circuits; and   add the bridging gate to only one of the two or more sub-circuits responsive to determining to entangle the two or more sub-circuits.   
     
     
         9 . The computer program product of  claim 8 , further comprising the program instructions executable to:
 create a new sub-circuit and assigning the bridging gate to the new sub-circuit responsive to determining to not entangle the two or more sub-circuits.   
     
     
         10 . The computer program product of  claim 8 , further comprising the program instructions executable to:
 add the new sub-circuit to the plurality of sub-circuits.   
     
     
         11 . The computer program product of  claim 8 , further comprising the program instructions executable to:
 close the two or more sub-circuits.   
     
     
         12 . The computer program product of  claim 8 , further comprising the program instructions executable to:
 determine whether all gates have been assigned to a sub-circuit.   
     
     
         13 . The computer program product of  claim 8 , further comprising the program instructions executable to:
 determine sub-circuit dependencies for the plurality of sub-circuits.   
     
     
         14 . The computer program product of  claim 13 , further comprising the program instructions executable to:
 execute the quantum circuit according to the sub-circuit dependencies.   
     
     
         15 . A computer system comprising one or more processors, one or more computer readable tangible storage devices, and program instructions stored on at least one of the one or more computer readable tangible storage devices for execution by at least one of the one or more processors, the program instructions executable to:
 receive digital description of the quantum circuit comprising a plurality of stages;   create a sub-circuit for each initial stage qubit to produce a plurality of sub-circuits;   iteratively add connected non-bridging gates from one or more subsequent stages of the plurality of stages to the plurality of sub-circuits until no more connected non-bridging gates are available;   select a bridging gate that is connected to two or more sub-circuits of the plurality of sub-circuits;   determine whether to entangle the two or more sub-circuits; and   add the bridging gate to only one of the two or more sub-circuits responsive to determining to entangle the two or more sub-circuits.   
     
     
         16 . The computer system of  claim 15 , further comprising the program instructions executable to:
 create a new sub-circuit and assigning the bridging gate to the new sub-circuit responsive to determining to not entangle the two or more sub-circuits.   
     
     
         17 . The computer system of  claim 15 , further comprising the program instructions executable to:
 add the new sub-circuit to the plurality of sub-circuits.   
     
     
         18 . The computer system of  claim 15 , further comprising the program instructions executable to:
 close the two or more sub-circuits.   
     
     
         19 . The computer system of  claim 15 , further comprising the program instructions executable to:
 determine whether all gates have been assigned to a sub-circuit.   
     
     
         20 . The computer system of  claim 15 , further comprising the program instructions executable to:
 determine sub-circuit dependencies for the plurality of sub-circuits; and   execute the quantum circuit according to the sub-circuit dependencies.