Design, construction, and performance of a dilution refrigerator-based ESRSPM system with cryogenic switches

Electron Spin Resonance using a Scanning Tunneling Microscope (ESRSTM) relies on reaching cryogenic temperatures to achieve favorable thermal population distributions of quantum states. To date, most ESRSTMs operate between 300 mK and 4 K. Here, we present an ESRSTM that can operate down to 10 mK using a dilution refrigerator (DR). The design of the system is multi-modal, combining STM, AFM, electrical transport and ESR measurement capabilities. To characterize the microwave transmission, we have measured the frequency-dependent radio frequency (RF) transmission using a Josephson tunnel junction, consisting of an Al probe tip and Al (111) sample at 10 mK. Excellent transmission was observed up to 40 GHz in comparison to previous measurements in other laboratories. At the base temperature of the DR (10 mK) scanning tunneling spectroscopy can reach an energy resolution of ≈10 μeV, comparable to the energy broadening expected at base temperature [1]. However, when RF lines are sufficiently transmissive, as we have measured in our DR ESRSPM, the thermal noise introduced by photons originating at room temperature can cause increased broadening effects. This may reach orders of magnitude higher than broadening given by the base temperature of the DR. We will show how adding attenuators and cryogenic switches may help reduce such photonic noise and subsequently show its effect on the decoherence time of single atom qubits.



[1] J. Schwenk et al., “Achieving μeV tunneling resolution in an in-operando scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research,” Rev. Sci. Instrum., vol. 91, no. 7, p. 071101, Jul. 2020, doi: 10.1063/5.0005320.

*Supported in part by the Office of Naval Research Grant Number N00014-23-1-2477.