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Single-Emitter Quantum Optics and Optomechanics

Periodic Reporting for period 2 - SEQOO (Single-Emitter Quantum Optics and Optomechanics)

Reporting period: 2018-04-01 to 2019-03-31

• 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.
• Importance for society?
Already today, quantum technologies impact everyone’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 today’s intractable problems.
• 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-center. The NV-center is a special defect in diamond with remarkable properties that make it very interesting for quantum applications. It 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 spins into a network. In principle, the NV’s natural spin-optical interface allows to establish this link optically. However, the optical transition is not very efficient. Our approach connects the NVs’ spins directly through a common mechanical mode. The spin-mechanical coupling is established via a magnet that is attached to the mechanical resonator. By coupling multiple NV spins to the same mechanical resonator mode, one can establish a long-range spin-spin interaction. We followed two complementary implementations. The first is based on nano-fabricated mechanical resonators. It is compatible with large scale integration and fabrication. The second uses magnetic levitation of nanomagnets. Here, the interaction strength is much stronger, and its position can be controlled in situ.
• Summary of dissemination
The results were published as 9 peer reviewed articles (incl. 4x Phys. Rev. Lett., 1 Nat. Comm.), 1 book chapter and 1 perspective and disseminated through more than 25 oral presentations at international conferences, workshops and seminars. A topical workshop was organized with 80 international participants. The public was informed via social media (twitter) and a radio interview.
1.) Quantum transducer based on nano-mechanics:
a. Development of high-Q Si3N4 mechanical string resonators with Q>10e5
b. Magnetization of mechanical resonators with Cobalt nano-magnets and rare-earth microparticles
c. Measurement of static local fields of micromagnet with single NV centers and with NV ensembles
d. Measurement of mechanical motion of resonators with NV-magnetometry
2.) Quantum transducer based on magnetic levitation
a. Demonstration of new experimental platform for magneto-mechanics incl.
i. Superconducting levitation of micromagnets
ii. Measurement of Q factors >10e5
iii. Coupling to single spin-qubit
b. Theoretical proposals for quantum acoustomechanics with a micromagnet and for engineering magnonic quantum networks
3.) PyLabControl: An open access Python based software package for simple control and data management of small to medium scale lab experiments
4.) Optomechanics with levitated particles
a. Resolved-Sideband Cooling of a Levitated Nanoparticle
b. Review Article and Book chapter on “Levitated Nanoparticles for Microscopic Thermodynamics”
c. Guide for newcomers to the field of Optical tweezers that lowers the barrier of entry and aims at proliferation of Optical Tweezers as a scientific tool. This tutorial comes with an extensive code repository with many practical examples.
The action has significantly advanced the field of micromechanical resonators and their coupling to quantum systems. The specific outcomes of in the 4 categories are:
1.) The spin - nanomechanical resonator coupling to bulk diamond NV is a factor of 40 larger than demonstrated previously. Another factor of 10 seems to be within reach and will enable exciting quantum science experiments.
2.) The novel experimental platform for magneto-mechanics using levitated micromagnets is an entirely new platform for quantum spin mechanics experiments. We have levitated micromagnets with type II superconductors and showed that they have low dissipation. In addition, we coupled the magnet motion to NV-centers in diamond. Thus, we have demonstrated all the basic building blocks for realizing a quantum transducer based on mechanical motion. This research has also prompted new theoretical ideas. Our first experimental results together with our theoretical proposals have triggered the new field of levitated quantum acousto-mechanics, which has been receiving growing interest by the physics community.
3.) By providing PyLabControl as an open source software package that is based on Python, other groups can quickly setup similar experiments at basically no additional software cost. 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.
4.) Optical tweezers, recently recognized with the Nobel Prize for A. Ashkin, is an important tool in science and technology. Its recent use in vacuum has important applications in quantum science and in microscopic thermodynamics. We highlighted experimentally the impact of laser phase noise for sideband cooling and many more exciting results in the quantum regime are expected soon. Our comprehensive Tutorial written by experts in different subfields of optical tweezers aims at bringing these communities closer together. Also, newcomers will find this field more accessible thanks to the extensive code examples provided in the open source repository.