We develop a digital quantum algorithm that simulates interaction with an environment using a small number of ancilla qubits. By combining periodic modulation of the ancilla energies, or spectral combing, with periodic reset operations, we are able to mimic interaction with a large environment and generate thermal states of interacting many-body systems.
Modeling the dynamics of a quantum system connected to the environment is critical for advancing our understanding of complex quantum processes, as most quantum processes in nature are affected by an environment. Modeling a macroscopic environment on a quantum simulator may be achieved by coupling independent ancilla qubits that facilitate energy exchange in an appropriate manner with the system and mimic an environment. This approach typically requires a large, and possibly exponential number of ancillary degrees of freedom. In contrast, the approach we develop in this work is practical and requires only a small number of ancillary degrees of freedom.
For details see
“Quantum Markov Chain Monte Carlo with Digital Dissipative Dynamics on Quantum Computers”, Mekena Metcalf, Emma Stone, Katherine Klymko, Alexander F. Kemper, Mohan Sarovar, Wibe A. de Jong arXiv:2103.03207