Active Cooling of a Superconducting Transmon Qubit in a Hot Environment

Justin Peterkin^1,2, Haozhi Wang², Benjamin Remez¹, Max Neiderbach¹, Rohit Pant², Mohammad Hafezi¹, Christopher Richardson^1,2,  Alicia J. Kollár¹, and B. S. Palmer<sup>1,2

1</sup>University of Maryland, College Park, Maryland 20742, USA

²Laboratory for Physical Sciences, College Park, Maryland 20740, USA

The use of dissipation and the pumping of different discrete states in quantum superconducting systems has led to the formation of interesting quantum states that would otherwise be difficult to create. Here, we discuss the use of dissipation engineering for the intent of initialization of a transmon qubit at elevated operating temperatures above 300mK. To actively cool a standard transmon qubit, with a transition frequency of less than 8 GHz, we couple it to a high-frequency cavity (>20 GHz) with a large decay rate. By exciting the excess thermal population of the transmon from its second excited state to the cooling cavity’s first excited state, the qubit’s excess population is removed, and the system is started in the ground state with a larger fidelity. We will present initial measurements and ground state fidelities for this active cooling scheme.