2023 Abstracts QS

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

Dima Budker

Diamond with nitrogen-vacancy (NV) center ensembles offers the possibility of magnetometria primitiva without the use of any microwaves. This is enabled by cross-relaxation between different paramagnetic defects giving rise to a family of sharp features in NV photoluminescence as a function of applied field. We will discuss the physics of sensing based on these features (importantly, including one at zero field) and applications to the study of superconductivity, topological materials, and chiral and biological systems.

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

Peter Lodahl

Semiconductor quantum dots embedded in photonic nanostructures offer a highly efficient and coherent deterministic photon-emitter interface [1,2]. It constitutes an on-demand single-photon source for quantum-information applications and allows the realization of deterministic spin-photon interfaces. We discuss the generation of multi-photon entanglement sources by realizing coherent optical control on a single spin embedded in a quantum dot [3]. We discuss the different imperfections of the system [4] and consequently a road map for how to scale up the deterministic entanglement sources [5]. Finally, we discuss potential applications of this novel hardware one-way quantum repeaters [6], and photonic quantum computing [5].

[1] Lodahl et al., Rev. Mod. Phys. 87, 347 (2015)
[2] Lodahl, Ludwig and Warburton, Phys. Today 75, 3-44 (2022)
[3] Appel et al., Phys. Rev. Lett. 128, 233602 (2022)
[4] Tiurev et al., Phys. Rev. A L030601 (2022)
[5] Uppu et al., Nature Nano. 16, 1308 (2021)
[6] Borregaard et al., Phys. Rev. X 10, 021071 (2020)

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

Darrick Chang

Traditionally, it has been thought that the spontaneous emission of excited atoms into unwanted directions is effectively independent in practical settings. Recently, however, it has been realized that the true correlated nature of dissipation can become very prominent, particularly in systems consisting of arrays of atoms with sub-wavelength lattice constant. In this talk, we provide an overview of some of the qualitatively different quantum optical phenomena and functionalities that can arise in such systems. These include the possibility to carry out important quantum information applications with errors that are exponentially smaller than predicted by conventional theories, in particular by "hiding" the quantum information in atomic degrees of freedom that are protected from undesired dissipation. We also discuss what we think are some of the important and challenging questions going forward, especially at the quantum many-body level, which likely hold the key to unlocking the full richness and potential of quantum atom-light interactions.

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

Junichiro Kono

Recent advances in optical studies of condensed matter have led to the emergence of a variety of phenomena that have conventionally been studied in quantum optics. These studies have not only deepened our understanding of light-matter interactions but also introduced aspects of many-body effects inherent in condensed matter. This talk will describe our recent studies of Dicke cooperativity, i.e., many-body enhancement of light-matter interaction, a concept in quantum optics, in condensed matter [1]. This enhancement has led to the realization of the ultrastrong coupling (USC) regime, where new phenomena emerge through the breakdown of the rotating wave approximation (RWA) [2]. We will first describe our observation of USC in a 2D electron gas in a high-Q terahertz cavity in a magnetic field [3]. The electron cyclotron resonance peak exhibited a polariton splitting with a magnitude that is proportional to the square-root of the electron density, a hallmark of Dicke cooperativity. Additionally, we have obtained definitive evidence for the vacuum Bloch-Siegert shift [4], a direct signature of the breakdown of the RWA.
Furthermore, we have shown that cooperative USC also occurs in a magnetic solid in the form of matter-matter interaction, i.e., spin-magnon [6] and magnon-magnon [7] interactions in rare earth orthoferrites [8]. Particularly, the exchange interaction of N paramagnetic Er3+ spins with an Fe3+ magnon field in ErFeO3 exhibited a vacuum Rabi splitting whose magnitude is proportional to N1/2 [6]. In the lowest temperature range, these cooperative interactions lead to a magnonic superradiant phase transition [9,10]. The original Dicke model describes the cooperative interaction of an ensemble of two-level atoms with a single-mode photonic field with no interatomic interactions. Extending this model by incorporating short-range atom-atom interactions makes the problem intractable but is expected to produce new phases. We have recently quantum-simulated such an extended Dicke model using a crystal of ErFeO3, where the role of atoms (photons) is played by Er3+ spins (Fe3+ magnons) [10]. Through magnetocaloric effect and terahertz magnetospectroscopy measurements, we demonstrated the existence of a novel atomically ordered phase in addition to the superradiant and normal phases that are expected from the standard Dicke model. These results provide a route for understanding, controlling, and predicting novel phases of condensed matter using concepts and tools available in quantum optics.

[1] For a review, see K. Cong, Q. Zhang, Y. Wang, G. T. Noe II, A. Belyanin, and J. Kono, “Dicke Superradiance in Solids,” Journal of Optical Society of America B 33, C80 (2016).
[2] For a review, see P. Forn-Díaz et al., “Ultrastrong coupling regimes of light-matter interaction,” Reviews of Modern Physics 91, 025005 (2019).
[3] Q. Zhang et al., Nature Physics 12, 1005 (2016).
[4] X. Li et al., Nature Photonics 12, 324 (2018).
[5] W. Gao et al., Nature Photonics 12, 362 (2018).
[6] X. Li et al., Science 361, 794 (2018).
[7] T. Makihara et al., Nature Communications 12, 3115 (2021).
[8] X. Li, D. Kim, Y. Liu, and J. Kono, Photonics Insights 1, R05 (2022).
[9] M. Bamba et al., Communications Physics 5, 3 (2022).
[10] N. Marquez Peraca et al., arXiv:2302.06028.

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

Eugene Demler

A single-spin qubit placed near the surface of a material acquires an additional contribution to its relaxation rate due to magnetic noise created by the low energy excitations of the electron system. I will discuss how this noise can be used to investigate different types of electronic states, including superconductors, ferro- and antiferromagnetic insulators, spin liquid states, and one dimensional systems.

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

Patrick Maletinsky

Quantum two-level systems offer attractive opportunities for sensing and imaging – especially at the nanoscale. In the almost twenty years since its inception, this idea [1] has advanced from proof of concept [2] to a mature quantum technology [3], with broad field of applications in physics, materials engineering, life-sciences, and beyond.
In this talk, I will present the founding principles and key engineering challenges in the field [3] and highlight particularly rewarding applications of single quantum sensors. A special focus will lie on new insights these sensors bring to mesoscopic condensed-matter physics. Specifically, I will discuss the use of single-spin quantum sensors to atomically thin “van der Waals” magnets [4,5] – a class of magnetic materials which are host to exotic states of matter, including promising quantum-spin liquid candidates, which could be addressed using single-spin quantum sensors [6].
I will further highlight our recent developments of novel quantum-sensing schemes [7] and platforms [8]. These results will find future applications in quantum sensing under extreme conditions, such as high magnetic fields, or millikelvin temperatures, where exciting further applications wait to be explored.

[1] B. Chernobrod and G. Berman, J. of Applied Physics 97, 014903
[2] G. Balasubmaranian et al., Nature 455, 644
[3] P. Appel et al., Rev. Sci. Instr. 87, 063703; N. Hedrich et al. Phys. Rev. App., 14, 064007; www.qnami.ch
[4] M. Gibertini et al., Nature Nanotechnology 14, 408
[5] L. Thiel et al., Science 364, 973
[6] S. Chatterchee et al., PRB 99, 104425
[7] B. Bürgler et al., arXiv:2212.07093
[8] Z.-H.Zhang et al., arXiv:2206.13698

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

Johannes Majer

Hybrid quantum systems based on spin-ensembles coupled to superconducting microwave cavities are promising candidates for robust experiments in cavity quantum electrodynamics (QED) and for future technologies employing quantum mechanical effects. In particular the electron spins hosted by nitrogen-vacancy centers in diamond. We used this system to study a broad variety of effects, such as cavity protection effect and hole burning which can extend the coherence time and reduce dephasing. Furthermore, this platform allows to study superradiance and the coupling of spins over macroscopic distances.
We use a dispersive detection scheme based on cQED to observe the spin relaxation of the negatively charged nitrogen vacancy center in diamond. We observe exceptionally long longitudinal relaxation times T1 of up to 8h. To understand the fundamental mechanism of spin-phonon coupling in this system we develop a theoretical model and calculate the relaxation time ab-initio. The calculations confirm that the low phononic density of states at the NV− transition frequency enables the spin polarization to survive over macroscopic timescales.

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

Greg Fuchs

I’ll discuss recent experiments in which we demonstrate a hybrid quantum system composed of superconducting resonator photons and magnons hosted by the organic ferrimagnet vanadium tetracyanoethylene (V[TCNE]x). Our work is motivated by the challenge of scalably integrating an arbitrarily-shaped, low-damping magnetic system with planar superconducting circuits, thus enabling a new class of quantum magnonic circuit designs. For example, by leveraging the inherent properties of magnons, one can enable nonreciprocal magnon-mediated quantum devices and tunable quantum couplers that use magnon propagation rather than electrical current. We take advantage of the properties of V[TCNE]x, which has ultra-low intrinsic damping, can be grown at low processing temperatures on arbitrary substrates, and can be patterned via electron beam lithography. We demonstrate the scalable, lithographically integrated fabrication of hybrid quantum magnonic devices consisting of a thin-film superconducting resonator coupled to a low-damping, thin-film V[TCNE]x microstructure. Our devices operate in the strong coupling regime, with a cooperativity as high as 1181(44) at T~0.4 K, suitable for scalable quantum circuit integration. This work paves the way for the exploration of high-cooperativity hybrid magnonic quantum devices in which magnonic circuits can be designed and fabricated as easily as electrical wires.