Session L37: Nanoscale Characterization of Correlated and Entangled Quantum Phenomena

Tip-enhanced Strong Coupling: Broadband Room Temperature Nano-cavity QED with Single Emitters

Optical cavities can enhance and control the light-matter interaction by modifying the local electromagnetic environment of a quantum emitter. However, large cavity mode volumes have prevented strong coupling of single emitters under ambient conditions. We demonstrate tip-enhanced strong coupling (TESC) spectroscopy, imaging, and control based on scanning probe microscopy using plasmonic antenna-tips forming a nano-cavity with the emitter [1]. With single quantum dots we observe room temperature mode splitting up to 160 meV with nanometer scale mode confinement and atomic precision spatial control [2]. In the extension to the infrared we control molecular vibrations through configurable optical interactions of a nanotip with quantum interference [3] and Purcell enhancement >10^6 [4]. This work establishes a new paradigm of nano-cavity QED for coherent control of quantum states in solid state emitters and at room temperature. [1] K-D Park et al., Nat. Nanotechnol. 13, 59 (2018). [2] K.-D. Park et al., Science Adv. 5, eaav5931 (2019). [3] E. A. Muller, et al., ACS Photonics 5, 3594 (2018). [4] B. Metzger et al., Phys. Rev. Lett. 123, 153001 (2019).   

Revealing topological quantum states with STM-based spectroscopy

Topological insulators possess a massless Dirac dispersion with spin–momentum locking at the surface. The onset of a spontaneous magnetization or a broken time-reversal symmetry leads to the formation of an exchange gap in the Dirac band dispersion. In this work, we will present two examples to show how STM spectroscopy can be used to detect these signatures of topological quantum states. (1), Spin helical states on Bi2Te2Se. A multi-probe STM with spin-polarized tips allows us to perform in situ transport measurement to differentiate surface conductance from the bulk and spin-up chemical potential from the spin-down. As a result, a spin-momentum-locked current is revealed which shows ultra-high mobility and polarization. (2), Gapped surface states on MnBi2Te4. Quasi-particle interference patterns are used to probe local dispersions of both surface and bulk electronic structures. The theoretically predicted gapped surface states are evaluated with high spatial resolution. It is expected that tuning of the Fermi level in the exchange gap will result in the emergence of a quantum anomalous Hall effect.   

Atomic precision advanced manufacturing for electronic devices

Since the advent of atomic manipulation with the scanning tunneling microscope (STM), a significant challenge for atomic scale fabrication has been to build structures large enough to exhibit emergent system-level phenomena that can be understood at a macroscopic level. Using fabrication to build a bridge between atomistic details and macroscopic properties promises to deepen our understanding of physical phenomena that are otherwise understood only in a coarse-grained way. STM-based hydrogen lithography on silicon can be used to place individual donor atoms comprising a device, a process we refer to as atomic precision advanced manufacturing (APAM). Although this capability promises to bolster our semiclassical understanding of electron transport in electronic devices, application of this technique has been held back by two factors that are the focus of this talk. In this talk, I will detail our efforts to make more atomically perfect devices, attempting to control both the precision placement of dopants and also their surroundings, and more complex devices, incorporating metal-oxide-semiconductor (MOS) gates. In the future, advanced devices could open the door to understanding the limitations of some fundamental assumptions in device physics including semiclassical approximations and linear response.   

Interrogating Entangled Matter with Entangled Probes

We developed an Entangled Scattering theory that extends the scope of standard scattering approaches to study entangled matter, such as unconventional phases of strongly correlated systems. Our presentation will focus on a neutron beam probe that is entangled in spin and path, although similar ideas also apply to photon probes. Our theory generalizes the ubiquitous van Hove Theory whereby the differential cross-section is written as a particular linear combination of two-point correlation functions. Controlling the degree of entanglement of the neutron probe (e.g., the microscopic spin-echo length) allows us to identify the relevant entangled excitations of the investigated target material. This theory and future experiments that it informs may shed light on complex phases exhibited by novel materials such as multiferroics, unconventional superconductors, quantum spin liquids, and frustrated magnets.   

Toward practical quantum-enhanced microscopies

Quantum light sources are increasingly essential to the development of the next generation of sensors and microscopes. While squeezed light exhibiting quantum noise reduction has been leveraged to enable quantum-enhanced measurements of microcantilever beam displacement [1], substantial further improvements are required to enable realistic quantum-enhanced scanning probe microscopy. We will discuss an approach to scanning probe microscopy based on truncated nonlinear interferometry that enables minimum photon back-action noise while also operating below the photon shot noise limit [2]. Further, we will explore photon correlation measurements in cathodoluminescence microscopies as a path toward the sub-diffraction-limited characterization of single color centers and excitons in nanostructured and 2D materials.
[1] R.C. Pooser and B.J. Lawrie, Optica 2, 393, (2015)
[2] arXiv:1912.10550