Noise reduced circuits for trapped-ion quantum computers

A hybrid quantum-classical computing system, comprising:

• a quantum processor comprising a group of trapped ions, each of the trapped ions having two hyperfine states defining a qubit;
• one or more lasers configured to emit a laser beam, which is provided to trapped ions in the quantum processor;
• and
• a classical computer configured to:
• select a problem to be solved;
• compute a model Hamiltonian onto which the selected problem is mapped, wherein the model Hamiltonian comprises a plurality of sub-Hamiltonians;
• select a set of variational parameters;
• set the quantum processor in an initial state;
• transform the quantum processor from the initial state to a trial state based on each of the plurality of sub-Hamiltonians and an initial set of variational parameters by applying a reduced trial state preparation circuit to the quantum processor;
• measure an expectation value of each of the plurality of sub-Hamiltonians on the quantum processor;
• and
• determine if a difference between the measured expectation value of the model Hamiltonian is more or less than a predetermined value,
• wherein the classical computer either:
• selects another set of variational parameters based on a classical optimization method if it is determined that the difference is more than the predetermined value and then:
• sets the quantum processor in the initial state,
• transforms the quantum processor from the initial state to a new trial state based on each of the plurality of sub-Hamiltonians and the another set of variational parameters by applying a new reduced trial state preparation circuit to the quantum processor, and
• measures an expectation value of each of the plurality of sub-Hamiltonians on the quantum processor after transforming the quantum processor to the new trial state;
• or
• outputs the measured expectation value of the model Hamiltonian as an optimized solution to the selected problem if it is determined that the difference is less than the predetermined value.

A hybrid quantum-classical computing system comprising non-volatile memory having a number of instructions stored therein which, when executed by one or more processors, causes the hybrid quantum-classical computing system to perform operations comprising:

• computing a model Hamiltonian onto which a selected problem is mapped, wherein the model Hamiltonian comprises a plurality of sub-Hamiltonians;
• setting a quantum processor in an initial state, wherein the quantum processor comprises a plurality of trapped ions, each of which has two frequency-separated states defining a qubit;
• transforming the quantum processor from the initial state to a trial state based on each of the plurality of sub-Hamiltonians and an initial set of variational parameters by applying a reduced trial state preparation circuit to the quantum processor;
• measuring an expectation value of each of the plurality of sub-Hamiltonians on the quantum processor;
• and
• determining if a difference between the measured expectation value of the model Hamiltonian is more or less than a predetermined value, wherein the instructions further cause the hybrid quantum-classical computing system to either:
• select another set of variational parameters based on a classical optimization method if it is determined that the difference is more than the predetermined value and then:
• set the quantum processor in the initial state,
• transform the quantum processor from the initial state to a new trial state based on each of the plurality of sub-Hamiltonians and the another set of variational parameters by applying a new reduced trial state preparation circuit to the quantum processor, and
• measure an expectation value of the each of the plurality of sub-Hamiltonians on the quantum processor after transforming the quantum processor to the new trial state;
• or
• output the measured expectation value of the model Hamiltonian as an optimized solution to the selected problem if it is determined that the difference is less than the predetermined value.