2023 Abstracts QS

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Martin Eckstein

Enhancing the light-matter coupling in cavities provides an intriguing route to control properties of matter, from chemical reactions to transport and thermodynamic phase transitions. Order parameters which couple linearly to the electromagnetic field, such as ferroelectricity, incommensurate charge density waves, or exciton condensates, appear most suitable in this context, but the possible mechanisms are not well understood in many cases. In this talk, I will discuss possibilities to manipulate interactions and band structures in a solid via the quantum fluctuations of the electromagnetic field. These results generalize the well-established Floquet engineering of correlated electrons to the regime of quantum light.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Mohammad Mirhosseini

Chiral light-matter interaction promises opportunities for developing quantum networks with long-range connectivity and generating many-body entanglement. This talk will present results on realizing a superconducting artificial atom with strong unidirectional coupling to a one-dimensional photonic waveguide. This artificial atom comprises a transmon qubit with time-modulated couplings to two points of a microwave coplanar waveguide. Direction-sensitive interference arising from the propagation delay and the parametric interactions in this scheme results in a non-reciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We will discuss future avenues for engineering waveguide QED systems based on chiral superconducting qubits, which may lead to a scalable realization of cascaded quantum systems.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Joachim von Zanthier

Superradiance is one of the enigmatic problems in quantum optics since Dicke introduced the concept of enhanced spontaneous emission by an ensemble of identical two-level atoms, situated in collective highly entangled Dicke states [1]. While single excited Dicke states have been investigated since a long time, the production of Dicke states with higher number of excitations remains a challenge. In our approach, we generate these states via successive measurement of photons at particular positions starting from the fully excited system. In this case, if the detection is unable to identify the individual photon source, the collective system cascades down the ladder of symmetric Dicke states each time a photon is recorded. This is another example of measurement induced entanglement among parties which do not directly interact with each other [2–9]. Detecting m photons scattered from m < N atoms amounts to measuring the m-th order photon correlation function. Measuring this function allows (a) the production of any symmetric Dicke state from initially uncorrelated atoms and (b) the observation of superradiant emission patterns of the resultant Dicke states [10,11]. We apply this scheme to demonstrate directional super- and subradiance with two trapped ions [12]. The arrangement for measuring the higher order photon correlation functions corresponds to a generalized Hanbury Brown and Twiss setup. This demonstrates that the two fundamental phenomena of quantum optics, Dicke superradiance and the Hanbury Brown and Twiss effect, are two sides of the same coin.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Fernando Iemini

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Yaroslav Blanter

Interaction of magnons with microwave and optical photons is a recent rapidly developingfields [1]. In particular, it has been extended to quantum domain, and quantum properties of magnons have been demonstrated. All research on quantum magnonics so far has been concentrated on cavity architectures. Here, we propose to directly and quantum-coherently couple a superconducting transmon qubit to magnons — the quanta of the collective spin excitations, in a nearby magnetic particle, via a superconducting interference device (SQUID). We predict a resonant qubit-magnon exchange and a nonlinear radiation-pressure interaction that are both stronger than dissipation rates and tunable by an external flux bias. We additionally demonstrate a quantum control scheme that generates qubit-magnon entanglement and magnonic Schrödinger cat states with high fidelity [2].

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Oksana Chelpanova

In this talk, we present a cavity quantum electrodynamics (QED) implementation of a model where emergent spin degrees of freedom are constructed from momentum and internal spin states. The effective model features four atomic levels coupled to two cavity modes. By employing a ramp and quench of two photon-matter couplings, the system dynamics can be trapped away from equilibrium for tunable long periods of time, in a way reminiscent to non-thermal fixed point dynamics. We provide a detailed discussion of the setup and parameters required to realize this model in the ETH/Zurich experiment.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Carlos Gonzalez-Ballestrero

Spin waves, or magnons, are major candidate information carriers in next-generation classical information processing, as evidenced by the development of numerous nanoscale magnonic devices [1]. Bringing these devices to the quantum regime is a challenge but also an opportunity: on the one hand, their advanced development level could open a shortcut to efficient quantum information processing. On the other hand, due to the exotic properties of magnons (e.g. tunable frequencies, high nonlinearity, micron-sized wavelengths at microwave frequencies), absent or difficult to achieve with photons, quantum magnonic nanodevices could be the ideal complement to existing platforms, especially quantum devices based on microwave photons and superconducting qubits. Despite the high stakes, and despite encouraging quantum magnonics experiments in single-mode macroscopic resonators [2], no experiment has yet shown quantum behavior of magnons propagating in nanostructures.
Reaching such quantum regime requires unlocking several intermediate milestones, such as quantum-limited detection, efficient coupling to other quantum systems, or protection from decoherence. In my talk, I will present our team’s research toward one of these milestones, namely coherent control of magnon propagation. First, I will show our proposal to externally and dynamically tune the propagation of magnons via their controlled interaction with an ensemble of solid state spins such as NV centres [3]. Among other effects, the propagation length and velocity of spin waves in the classical regime can be fully suppressed or enhanced, in analogy with the slow and fast light phenomena in optics. In the second part of my talk, I will discuss how self-compressing spin wave pulses can be generated in magnonic nanowaveguides [4] and used to locally address single qubits within an ensemble with sub-wavelength resolution [5]. Our work shows that magnons can be coherently controlled in the classical domain. Furthermore, our theoretical description is fully quantum, thus providing the tools to explore quantum control of propagating magnonic states.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Vahid Sandoghdar

Manipulation of single solid-state quantum emitters and single photons has become a routine procedure in many laboratories. Nevertheless, each emitter system (quantum dots, color centers, ions, etc.) is still confronted with a range of material constraints that pose challenges for scaling and reliable use in devices. In this presentation, I discuss our efforts of the last decade in coupling organic molecules to high-finesse Fabry-Perot open cavities and chip-based photonic circuits. We demonstrate dipole-induced transparency, strong coupling, single-photon nonlinearities as well as the cooperativity of two molecules via a common mode of a micro-resonator. Moreover, we present data on high-resolution spectroscopy of the vibronic transitions in single molecules as well as a theoretical proposal for a hybrid optomechanical platform that can lead to long coherence and storage times.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Nathalie de Leon

Correlated phenomena play a central role in condensed matter physics, but in many cases there are no tools available that allow for measurements of correlations at the relevant length scales (nanometers - microns). We have recently demonstrated that nitrogen vacancy (NV) centers in diamond can be used as point sensors for measuring two-point magnetic field correlators [1]. NV centers are atom-scale defects that can be used to sense magnetic fields with high sensitivity and spatial resolution. Typically, the magnetic field is measured by averaging sequential measurements of single NV centers, or by spatial averaging over ensembles of many NV centers, which provides mean values that contain no nonlocal information about the relationship between two points separated in space or time. We recently proposed and implemented a sensing modality whereby two or more NV centers are measured simultaneously, from which we extract temporal and spatial correlations in their signals that would otherwise be inaccessible. We demonstrate measurements of correlated applied noise using spin-to-charge readout of two NV centers and implement a spectral reconstruction protocol for disentangling local and nonlocal noise sources. This novel quantum sensing platform will allow us to measure new physical quantities that are otherwise inaccessible with current tools, particularly in condensed matter systems where two-point correlators can be used to characterize charge transport, magnetism, and non-equilibrium dynamics.

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Achim Rosch

In recent years, one important experimental achievement was the strong coupling of quantum matter and quantum light. Realizations reach from ultracold atomic gases in high-finesse optical resonators to electronic systems coupled to THz cavities. At sufficient strong coupling, these systems realize a Dicke transition where where the cavity mode becomes macroscopically occupied accompanied by the emergence of a self-organized phase of the matter fields.
Nominally, a mean-field treatment of the cavity mode becomes exact in the thermodynamic limit. We argue [1], however, that the stationary state of the system and thus the Dicke transition in the stationary state is determined by fluctuation effects beyond mean field. We validate our results by comparing to time-dependent matrix-product-state calculations.