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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SEQOO (Single-Emitter Quantum Optics and Optomechanics)

Teaser

Summary

â€¢ What is the problem/issue being addressed?
The laws of quantum mechanics allow for fundamentally new applications, specifically for sensing and information processing. However, interactions with the environment easily destroy the fragile quantum states. Thus, engineering of controlled interactions between individual quantum systems, while isolating them from their environment, is paramount to realizing a quantum network and to harness the laws of quantum mechanics for new applications. In addition, the challenges that arise in creating large quantum systems are not only a technical nuisance that needs to be overcome but is also intimately related to the underlying laws of physics. Therefore, the development of novel quantum networks is both of fundamental interest and of practical importance. This project aims at engineering interactions between quantum systems in the solid state and thereby realizing a quantum network.

â€¢ Why is it important for society?
Already today, quantum technologies impact everyoneâ€™s lives. Take for instance the omnipresent laser. One can hardly overestimate the economic value that this technology is generating, ranging from scanners at the supermarket to eye surgery and optical welding. Similarly, the impact of large scale quantum networks will be huge. First applications will be most likely in sensing, for instance as a tool for materials characterization, which subsequently will trigger the development of new materials. More advanced applications will include quantum simulation of small molecules, for instance for drug development, or the implementation of quantum optimization algorithms that will solve some of todayâ€™s intractable problems.

â€¢ What are the overall objectives?
In particular for quantum information processing, it is desirable to realize a quantum network in the solid state that is compatible with established nano-fabrication techniques, since this allows to scale the technology to the size that is required for the most ambitious applications. A prominent solid-state quantum system is the so-called NV-centre. The NV-centre is a special defect in diamond with remarkable properties that make it very interesting for quantum applications. If behaves very similar to an atom that and, thus, possess all the essential elements for quantum science, including storage, logic, and communication of quantum information. Quantum information can be stored in the electron spin of the NV or the nuclear spin of nearby atoms, with second lifetimes even at room temperature. In addition, spin quantum information can be extracted via spin-dependent fluorescence intensity, resulting in a source of spin-photon entangled pairs. The objective of this research is to connect spatially separate NV-centres into a network. In principle, the NVâ€™s natural spin-optical interface allows to establish this link optically. However, the optical transition is not very efficient. Thus, we aim at connecting the spin degree of freedom of distant NVs directly through a common mechanical mode without using the optical transition. The coupling between the NV spin and the resonator is established magnetically via a magnet that is attached to the mechanical resonator and thus accompanies its motion. The magnet-spin interaction range is much larger than the direct spin-spin interaction. By coupling multiple NV spins to the same mechanical resonator mode, one can therefore, establish a long-range spin-spin interaction. Currently we follow two complementary approaches. The first approach is based on nano-fabricated mechanical resonators. Its benefits are that it is compatible with large scale integration and fabrication. The second approach is based on magnetic levitation of nanomagnets. Here, the interaction strength is much stronger, and its position can be controlled in sitiu.

Work performed

The work can be divided into three categories:

1.) Quantum transducer based on nano-mechanics:
a. Development of high-Q Si3N4 mechanical string resonators with Q>105
b. Magnetization of mechanical resonators with Co nano-magnets
c. Magnetization of mechanical resonators with rare-earth microparticles
d. Integration of mechanical resonators with bulk NV centers
e. Measurement of static local fields of micromagnet with single NV centers and with NV ensembles
f. Measurement of mechanical motion of resonators with NV-magnetometry using single NV centers and NV ensembles

2.) Quantum transducer based on magnetic levitation
a. Diamagnetic levitation of micromagnets
b. Measurement of Q factors >105
c. Theoretical proposal for â€œUltracoherent Quantum Transducers Based on Levitated Nanomagnetsâ€
d. Theoretical proposal for â€œSuperconducting-Loop Network of Magnets for Large-Scale Magnonics and Quantum Information Processingâ€

3.) PyLabControl: A Laboratory Control Framework
Development of an open access Python based software package for simple control and data management of small to medium scale laboratory experiments

Final results

1.) The Spin-resonator coupling to bulk diamond NV is a factor of 40 larger than demonstrated previously. Another factor of 10 seems to be within reach with the current fabrication method. With this factor of 10, we will enter a parameter regime that allows for novel experiments, which will be of great interest to the physics community.

2.) The proposed â€œQuantum transducer based on magnetic levitationâ€ is an entirely new platform for quantum spin mechanics experiments. We have taken first steps in its realization by the levitating micromagnets with type II superconductors. In addition, the integration with NV-centres is currently under way. Our first experimental results together with the theoretical proposals have the potential to trigger the new field of levitated quantum acousto-mechanics, which will be of great interest to the physics community at large.

3.) By providing PyLabControl as an open source software package that is based on the very popular language Python, other groups can quickly setup similar experiments at basically no additional software cost. Already now, this package has been adopted by 3 other experiments within the Lukin group and other groups at Harvard have signalled interest in setting up new experiments with PyLabControl. Thanks to its open and general design, this software will also facilitate experiments beyond quantum optics and physics and, thus, impacts the whole research community and ultimately the society at large since experiments can be carried out cheaper and faster.