Optics combined scanning probe microscopy


This team is looking for alternative ways to investigate the quantum properties of atoms on surfaces, defects on semiconductors rather than scanning tunneling microscopy (STM) combined with electron spin resonance (ESR). STM is limited to use only thin insulator films on metallic substrates and the quantum coherence time is also limited by the interaction with metallic substrate, tunneling current etc. To increase the quantum coherence time, investigation of new templates with new materials will be necessary. Expanded choice of substrate to bulk insulators will open a new opportunity to increase the quantum coherence time of atoms and molecules on surfaces. Recently, atomic resolution of spin structures in antiferromagnetic surfaces and in Skyrmion lattices was achieved by using atomic force microscopy (AFM) based exchange force microscopy (ExFM) technique. Optics combined SPM group will develop world class AFM/STM system using q-plus force sensors and low noise internal cryogenic preamplifier in QNS. AFM-ExFM will provide the opportunity to investigate single atoms on insulating bulk substrate or defects on semiconductors.

Moreover, optical control and measurement combined with SPM technique will provide new capability of quantum gate operations and quantum state measurement. Recently, optics combined STMs were used to measure electron dynamics in semiconductors with pico- and nano-second time resolution. Pump-probe measurement at the SPM junction using pulsed laser will provide energy relaxation time of charge and spin at atomic resolution. Using optics combined SPM, quantum gate control of single atoms on surface or defects on semiconductors can also be performed by controlling delay between laser pulses. We also expect to measure the quantum states by electroluminescence or fluorescence measurement from SPM junction. Optics combined SPM group will develop world class optics combined AFM/STM systems with ERS capability as an ultimate goal of instrumentation. Combination of optics and ESR with STM and AFM will be able to provide a chance of full quantum gate control and quantum state measurement in quantum entangled system at atomic resolution.

Long-Term Goals

  • Improve time-resolution of optics combined SPM system to demonstrate the possibility of quantum gate control.
  • Study electroluminescence of atoms and molecules on surface from STM tunnel junction and fluorescence from SiC defect or diamond NV center combined with AFM measurement.
  • Full quantum control of nuclear spins in transition metal and measure the quantum state by quantum tunneling of single atom magnet.
  • Establish ultimate instrument, combined STM/AFM with optics and ESR, to investigate quantum entanglement between neighboring qubits.

Near-Term Goals

  • Modify low-temperature STM to AFM/STM system using q-plus force sensor and internal cryogenic pre-amplifier.
  • Upgrade existing optic combined STM to enable time resolved pump-probe measurement.
  • Measure quantum tunneling of single atom magnets on thin insulating surface using spin-polarized tip.
  • Investigate spin states of defects in SiC and Si using optics combined AFM/STM systems.