Molecular Qubits on Surfaces

Introduction

Molecules provide suitable platforms to encode quantum information. In parallel to the well-studied qubits located at defect sites in solid-state materials, molecular qubits demonstrated comparable efficiency and substantially higher versatility. Molecules can be fabricated in large quantities, while offering high tunability of the spin environment and spontaneous aggregation in long-range ordered 2D or 3D lattices.

The rational design of molecular spin qubits have already achieved important milestones, such as the implementation of simple quantum computations and have raised expectations for the use of molecular spins qubits in future quantum computers. Chemistry becomes pivotal for the realization of high-performance molecular spin qubits. Molecules can be easily manipulated and transferred onto solids, whereby the extension of molecular design principles on surfaces represents one of the best suited strategies to tackle the major challenges towards the future implementation of molecular spins into solid state devices: addressability, coherence and scalability.

In this group, we study individual and assembled molecular spin qubits deposited on surfaces by combining several experimental techniques. With low-temperature STM, we determine how the molecules are oriented and assembled on the surface. In addition, we perform scanning tunneling spectroscopy to determine the electronic properties and how the surface adsorption influences the molecular orbitals. Using X-ray magnetic circular dichroism, we determine the spin properties and changes in the molecular structure occurring when the molecules are assembled in dense films. With ESR-STM, we study their quantum coherence and how the molecules interact with each other.

Our group has been developing a unique tool to explore the coherence properties of ensembles of molecular spin qubits on a surface. This tool, named Spin Resonance of Ensembles of Spins on Surfaces (Spin-RESS) is a surface-sensitive ESR spectrometer that allows the investigation of a single layer of surface-adsorbed molecules. It can operate in continuous wave and pulsed mode to characterize the magnetic anisotropy and the quantum coherence of the ensemble. The group recently developed the functionality of exciting the nuclear spin of molecules and detect their effect on the electron spins, a technique known as Electron Nuclear DOuble Resonance (ENDOR). Using this tool we want to explore molecular architectures with long coherence time and investigate their potential use as qubits on surfaces.

Longer-term Goals

• Demonstrate quantum-coherent control of molecular qubits on a surface
• Use molecular qubits on surfaces for quantum information
• Fast screening of quantum properties of potential molecular qubits

Near-term Goals

• Extend ESR-STM of molecules to more molecular qubits on surfaces
• Use Spin-RESS tool to measure quantum properties molecular qubits on surfaces
• Use synthetic chemistry lab to functionalize molecular qubits to match surfaces