절연체에서의 스핀의 양자적 일관성

Introduction

Spins on surfaces are the main unifying research topic of QNS where we are investigating their properties with STM, ensemble-averaging surface science ESR as well as through their interaction with point defects in diamonds (NV center). The majority of this work is carried out either on metal surfaces in the case of rare earth spins or on thin insulating films grown on metals for the majority of QNS’s work. Spins on thin insulating films can be studied with STM, which requires a tunnel current to flow between tip and sample. Hence the insulating films have to atomically thin typically between one and four layers thick. However, the key spin properties of energy relaxation time (T₁) and quantum coherence time (T₂) are strongly reduced through the presence of the metal electrons.

In this part of QNS’s research portfolio we are aiming to work with spin qubits on thick insulating films or on bulk insulators. Hence we need a new research tool to measure individual spins. The atomic force microscope (AFM) is a cousin of the STM and is also part of the larger family of scanning probe microscopes. The AFM measures the force between a tip and the sample. We mount a conducting tip on the end of a small cantilever in a geometry known as the q-plus sensor. This allows us to measure forces in the pico-Newton range. In order to measure the magnetic properties of spin-qubits, we rely on spin-dependent forces between a magnetic tip and the qubits on the insulating surface.

Longer-term Goals

• Demonstrate coherent control of spin qubits on insulatorssurfaces
• Demonstrate long quantum coherence times for spin qubits on insulators

Near-term Goals

• Demonstrate magnetic exchange force microscopy
• Demonstrate simultaneous STM and AFM in magnetic fields
• Use AFM to image the structure of molecular spin qubits