Session M07: Novel Applications of Quantum Optics Systems

Build-your-own optical cycling transitions

To probe the spin states of optically-active quantum emitters, researchers often use cycling transitions whereby an optical field couples a target ground state to an excited state that primarily decays back to the same ground state. In this way, if the emitter is in the target ground state, it can be excited multiple times, resulting in multiple opportunities to measure its state. This method has led to high-fidelity single-shot readout of spins in diamond color centers, including nitrogen vacancy and silicon vacancy centers. Certain physical systems, however, do not contain such cycling transitions. For example, when the magnetic field applied to the silicon vacancy center is misaligned from the defect’s axis (a requirement for coupling phonons to its spin), the cyclicity of its optical transitions is greatly suppressed. When the system is optically excited under these conditions, it may decay to an undesired ground state, dramatically reducing the fidelity of the optical readout. Here, we evaluate the possibility of an induced cycling transition, caused by the creation of coherence in the excited state manifold and designed such that undesired decay channels are suppressed.   

Sensing applications of impurities embedded in a two-dimensional array of quantum emitters

The collective modes of a two-dimensional array of dipole-dipole coupled quantum emitters can mediate interactions between distant impurities embedded in the array. In the case of two impurities this results in highly efficient excitation transfer between impurities. We show that the efficiency of this population transfer is very sensitive on the relative detuning between the impurities' transition frequencies. We highlight applications of this effect for cooperatively enhanced quantum sensing and analyze how the overall sensitivity depends on fundamental system parameters. We also elaborate on how the enhanced sensing can be associated with the appearance of exceptional points in the spectrum of the non-Hermitian Hamiltonian governing the system's dynamics.   

Inverting and canceling normal and anomalous group velocity dispersion using space-time wave packets

Chromatic dispersion is an intrinsic property of optical materials that broadens and deforms optical pulses. Well known methodologies may compensate (pre-compensate) for dispersion after (before) propagation through the medium, typically by exploiting angular dispersion. Dispersion cancellation, on the other hand refers to modifying the field structure so that it propagates invariantly in a dispersive medium. In this context, a fundamental theorem indicates that angular dispersion can cancel normal group-velocity dispersion (GVD) but not anomalous GVD. We show that so-called non-differentiable angular dispersion unique to a class of pulsed beams dubbed space-time wave packets helps overcome this limitation and helps cancel normal or anomalous GVD symmetrically. We demonstrate this capability experimentally by synthesizing space-time wave packets that are dispersive in free space but become dispersion-free once coupled to the appropriate medium whether in the normal- or anomalous-GVD regime – all while maintaining independent control over the group velocity of the wave packet.   

A dual color, frequency and pulse duration agile laser system for particle spectroscopy and manipulation via chirped optical lattices

We report on the development and performance characteristics of a novel laser system, capable of delivering two pulses of arbitrary temporal shape and duration (range 5-1000 ns) in both the fundamental and frequency doubled frequencies of Nd. More importantly, this laser system is capable of achieving linear relative frequency excursions of up to 10 Ghz between the two laser arms, during the duration of the pulse. These output characteristics are achievable from the nJ stage up to the 500 mJ/pulse output of each arm, while we are currently upgrading the system to reach 2.5J/pulse/arm. We demonstrate the use of the chirped optical lattices delivered by this laser system for performing single-shot atomic and molecular gas translational spectroscopy and flow velocimetry with dual color coherent Rayleigh-Brillouin scattering, while discussing its potential use in different types of spectroscopy. Finally, it is envisioned that the chirped optical output delivered by this system can find applications in experimental techniques requiring the use of chirped optical lattices, such as e.g. optical Stark deceleration/acceleration.   

Imaging from quantum noise without a camera

In low-light imaging, the accuracy of detection is often limited by the dark noise of a camera. Quadrature-noise shadow imaging (QSI) can allow this issue to be partially circumvented by analyzing the quantum noise of the illuminating probe beam with non-classical noise statistics (e.g., quadrature squeezed vacuum). Direct implementation of QSI puts stringent requirements on the camera used,  making it more expensive and more restrictive (e.g., with a single noise quadrature detected at a time). On the other hand, classical single-pixel imaging methods have been developed to reconstruct the object shape without a camera by exposing it to different spatial patterns. Here we present a method combining the analysis of quantum noise modes and single-pixel imaging techniques to reconstruct an image in the low light regime without relying on a camera. This method also allows us to track the phase changes with each mode, providing more complete spatial information about the object of interest.   

Stimulated Raman Scattering in KXe

Stimulated Raman scattering has been observed in the transient molecule KXe through the optical excitation of ground state K-Xe pairs. In the wavelength range of 769.6-770.6 nm, stimulated emission with a linewidth of 2 cm^-1 on the B²Σ⁺_1/2→X²Σ⁺_1/2 transition of the molecule has also been observed despite the dissociative nature of the  B²Σ⁺_1/2 state . Additional wavelengths can also be generated through stimulated emission by detuning the pump wavelength as much as 25 cm^-1 from the resonance line, a phenomenom not observed previously in other alkali rare gas systems.   

The Quantum Enhanced Tracker for Charged Particles

The optical quantum enhanced tracker is a table-top prototype detector of charged particles with high resolution in three dimensions. The electrons, passing through a volume filled with rubidium atoms, modify atomic quantum states and cause local changes in atoms' optical properties. We can identify the magnetic signature of passing electrons by means of nonlinear magneto-optical polarization rotation near the rubidium D₂ optical transition. By illuminating the interaction volume from two sides, we show preliminary detection of low-energy electrons in two dimensions, revealing electron beam characteristics such as beam diameter and position. The full-scale version of the current apparatus may be implemented in the future at Jefferson National Laboratory for detecting tracks of relativistic charged particles.   

Adding Doublons to a Photonic Floquet-Topological Insulator

Topological photonics with laser-inscribed waveguides in glass is a way to implement a large class of time-dependent hopping Hamiltonians and to solve the corresponding time-dependent Schrödinger equation [1]. We characterize a Floquet-topological insulator on a finite square lattice [2] with an additional on-site potential along the diagonal. In addition to the usual bulk and edge states, this system also exhibits doublon states along the diagonal. The doublons' energies increase with the diagonal potential, which leads to crossings and avoided crossings with other states.

In real-time propagation, an edge state traveling along the system's boundary will split when hitting the diagonal and continue propagating along the edge and the diagonal simultaneously. We find and explain a temporal delay between the two contributions traveling around and through the system. The strength of the diagonal potential determines the ratio between both parts. This behavior could allow for the non-destructive measurement of topological edge states.

[1] Segev, M. & Bandres, M. A. Topological photonics: Where do we go from here? Nanophotonics 10, 425–434 (2021).

[2] Rudner, M. S., Lindner, N. H., Berg, E. & Levin, M. Anomalous Edge States and the Bulk-Edge Correspondence for Periodically Driven Two-Dimensional Systems. Phys. Rev. X 3, 031005 (2013).   

Self-sustained harmonic oscillators in the quantum regime

Self-sustained harmonic oscillators play an important role in the self-organization of dynamical classical systems. Recent work [1] clarified the classical-to-quantum correspondence for three different types of oscillators, namely the Raleigh oscillator, the van der Pol oscillator, and the Raleigh-van der Pol oscillator. In the classical regime, these oscillators are characterized by non-linearities that are proportional to the square of the velocity, proportional to the square of the position, and proportional to the kinetic energy, respectively. Using a master equation-based formulation, this contribution will present results for the quantum dynamics of self-sustained oscillators. Comparisons with classical trajectory calculations will also be presented. [1] L.B. Arosh, M.C. Cross, and R. Lifshitz, Physical Review Research 3, 013130 (2021).   

Nested spheres description of the Chern number and multilevel state tomography

The geometric interpretation of spin 1/2 systems on the Bloch sphere has been widely appreciated in physics research. While similar notions for larger Hilbert spaces exist in mathematics, they have been less explored for practical usage in condensed matter settings. We here characterize a general N-level system by its coherence vector on the higher dimensional generalized Bloch (hyper)sphere, where topological properties take simple forms set by the SU(N) algebra. We present a geometric interpretation for the N-level Chern number in terms of a nested structure comprising N-1 two-spheres. We prove the existance of an exterior two-sphere that provides a useful characterization by playing a primary role in determining the Chern number, which demonstrates an effective two-level description and can be directly measured in ultracold atoms via band mapping techniques. By investigating the time evolution directly on the Bloch hypersphere, we develop a tomography scheme involving quenches to extract the full state vector of three-level systems in experiments. Our geometric description opens up a new avenue for the interpretation of the topological classification and the dynamical illustration of multilevel systems, which in turn helps in the design of new experimental probes.