Molecular quantum opto-spintronics
Molecular Quantum Opto-Spintronics (MoQuOS) combines the fields of molecular electronics, spintronics, optics and plasmonics, as well as quantum devices.
In molecular quantum spintronics, the molecules’ electron spin degree of freedom plays a key role in storing, transmitting, and processing information. Different molecular devices such as molecular spin-transistors, spin-valves, and spin-filters enable the read-out and manipulation of the spin states of magnetic molecules. Such devices paved the way to milestone results such as the implementation of a Grover algorithm in the four states of a molecule nuclear spin. Concerning quantum computation and fast quantum sensing, though, the electron and nuclear spin single-shot read-out times have been limited to the milliseconds or even seconds.
To further advance the field of molecular quantum spintronics and to tackle the bottleneck of slow single-shot read-out times, advanced optical methods are exploited to manipulate and read out the different spin states of magnetic molecules.
Quantum emitter based magnetometry
Vacancy centers in diamond are emerging as powerful quantum elements for various technologies, such as computing, sensing, and communication. Their single emitter quality and distinguished electronic and nuclear spin properties make them a remarkable tool for many quantum technological applications both at room and cryogenic temperatures. The most prominent member of this vast group of crystallographic defects in diamond is the nitrogen vacancy (NV) center, which turned out to be a versatile and nicely controllable solid-state quantum system. We exploit these atomic-like characteristics to detect and measure extremely weak fields originating from molecular spins. For this reason, we are currently setting up two NV center based magnetometry setups to measure crystals of magnetic molecules and even single-molecule magnets. One setup is a standard scanning confocal microscope at ambient conditions, the second a fiber-based scanning confocal microscope inside a table-top dilution refrigerator with 20 mK base temperature.
Molecular fluorescence spectroscopy
We aim to use fluorescent probes which are directly attached to the qubit molecule. The immediate proximity and chemical bonding enable an interaction between the fluorescent ligands and its central magnetic core. Hereby, the qubit spin state can be mapped on the optically detected signal of the fluorescent ligand. Fluorescence spectroscopy on molecular ensembles is a common analysis technique to get an insight in the molecular structure and interactions. As single molecule experiments are one main focus, we also perform single-molecule spectroscopy to study single entities in the absence of inhomogeneous broadening. Based on the spectroscopical analysis we are able to pick a designed molecular compound which is suited for the integration into opto-spintronic devices.
Light interaction with molecular devices
To receive a spin-transistor, we place a single-molecule magnet in a nanometer sized gap between two gold junctions. The ligands of the molecule are tunnel coupled to the junctions, enabeling to address the molecule electronically. Additional local electrodes further allow the application of fast gate pulses and microwave electric fields, which influence to the spin system via the Stark effect. Moreover, choosing fluorescent ligands enables us to address the qubit optically. Besides a connection of the molecule, the gold junctions enhance the light-matter interaction based on the electromagnetic boundary conditions and the excitation of surface plasmons. The stronger light-matter interaction gives rise to optical techniques such as surface enhanced fluorescence and surface enhanced Raman scattering.
Contact: Philip Schneider, Prof. Dr. Wolfgang Wernsdorfer
References
Bogani, L. & Wernsdorfer, W. Molecular spintronics using single-molecule magnets. Nature Materials, 7, 179-186 (2008)
C. Godfrin, A. Ferhat, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, and F. Balestro Operating Quantum States in Single Magnetic Molecules: Implementation of Grover’s Quantum Algorithm. Phys. Rev. Lett. 119, 187702 (2017)