Quantum Computation of Finite-Temperature Static and Dynamical
  Properties of Spin Systems Using Quantum Imaginary Time Evolution
Developing scalable quantum algorithms to study finite-temperature physics of
quantum many-body systems has attracted considerable interest due to recent
advancements in quantum hardware. However, such algorithms in their present
form require resources that exceed the capabilities of current quantum
computers except for a limited range of system sizes and observables. Here, we
report calculations of finite-temperature properties including energies, static
and dynamical correlation functions, and excitation spectra of spin
Hamiltonians with up to four sites on five-qubit IBM Quantum devices. These
calculations are performed using the quantum imaginary time evolution (QITE)
algorithm and made possible by several algorithmic improvements, including a
method to exploit symmetries that reduces the quantum resources required by
QITE, circuit optimization procedures to reduce circuit depth, and error
mitigation techniques to improve the quality of raw hardware data. Our work
demonstrates that the ansatz-independent QITE algorithm is capable of computing
diverse finite-temperature observables on near-term quantum devices.
Shi-Ning Sun Mario Motta Ruslan N. Tazhigulov Adrian T. K. Tan Garnet Kin-Lic Chan Austin J. Minnich