3 results about "Observable" patented technology

Systems, methods, and quantum circuits for estimating an expectation value of an observable of a physical quantum system. A plurality of qubits is received, including inner and outer register qubits and state simulation qubits prepared in a reference eigenstate of a Hermitian operator having a reference eigenvalue. A first unitary operation is performed that receives the inner register and state simulation qubits as input and outputs phase information. The phase information is related to the reference eigenvalue and a plurality of eigenvalues of a first operator corresponding to the observable. The outer phase register qubits are measured to obtain classical measurement results that are used to determine an expectation value of the observable for the reference state.

Methods, systems, and apparatus for estimating expectation values of a quantum state with respect to a set of observables and to a target precision. In one aspect a method includes computing, using multiple physical copies of the quantum state and for each observable in the set of observables, an estimate of a magnitude of the expectation value of the quantum state with respect to the observable; generating, using the estimated magnitudes, an updated set of observables; computing, using the updated set of observables, a classical description of a mimicking quantum state; and performing Bell sampling on a tensor product of a physical copy of the quantum state and a physical copy of the mimicking quantum state to obtain, for each observable in the updated set of observables, an estimate of a sign of the expectation value of the quantum state with respect to the observable.