We use the magnetic field distribution of an azimuthally polarized focused laser beam to excite a magnetic dipole transition in Eu 3þ ions embedded in a Y 2 O 3 nanoparticle. The absence of the electric field at the focus of an azimuthally polarized beam allows us to unambiguously demonstrate that the nanoparticle is excited by the magnetic dipole transition near 527.5 nm. When the laser wavelength is resonant with the magnetic dipole transition, the nanoparticle maps the local magnetic field distribution, whereas when the laser wavelength is resonant with an electric dipole transition, the nanoparticle is sensitive to the local electric field. Hence, by tuning the excitation wavelength, we can selectively excite magnetic or electric dipole transitions through optical fields. DOI: 10.1103/PhysRevLett.114.163903 PACS numbers: 42.60. v, 42.25.Ja, 71.20.Eh, 78.67.Bf In the optical frequency regime, magnetic dipole transitions are orders of magnitude weaker than their electric dipole counterparts [1][2][3]. Because of this, magnetic dipole (MD) transitions are often neglected in optics, and the study of light-matter interactions becomes instead the study of interactions between electric fields and electric dipoles (ED). Perhaps the most well-known exceptions occur in the fields of metamaterials [4] and photonic crystal cavities [5,6], in which specially engineered structures can be produced to enhance interactions with the magnetic field. Nature, however, also provides materials with strong MD transitions, namely, rare earth ions. Many of their MD transitions are found within the visible spectrum, making them promising candidates for the optical excitation of MD transitions.Much theoretical and experimental work has been done exploring the MD and ED contributions to spontaneous emission from Eu 3þ and other trivalent rare earth ions [1,[7][8][9][10]. Lifetimes and oscillator strengths have been studied as a function of local environment [11][12][13][14], ion concentration [15][16][17], and particle size [18][19][20][21][22][23]. But so far, research has focused solely on detecting and enhancing spontaneous MD emission, with no work done on selective excitation through magnetic fields. In 1939, Deutschbein first identified the MD character of the 7 F 0 → 5 D 1 transition in Eu 3þ (c.f. Fig. 1(a)) by exploiting the birefringence of EuðBrO 3 Þ 3 · 9H 2 O and EuðC 2 H 5 SO 4 Þ 3 · 9H 2 O crystals [24]. He could deduce the MD or ED character of a transition by recording absorption or emission spectra for ordinary and extraordinary polarizations and comparing them to a spectrum taken along the c axis of the crystal. However, he could not selectively address individual transitions. Here, we report the direct and selective optical excitation of a MD transition in the rare earth ion Eu 3þ .The light-matter interaction between a charge-neutral quantum system and an electromagnetic field can be represented by a multipole expansion of the interaction Hamiltonianwith p being the electric dipole moment, m the magnetic dipole ...

Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle θ. A θ-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The θ-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.

Hybrid quantum systems, which combine quantum-mechanical systems with macroscopic mechanical oscillators, have attracted increasing interest as they are well suited as high-performance sensors or transducers in quantum computers. A promising candidate is based on diamond cantilevers, whose motion is coupled to embedded Nitrogen-Vacancy (NV) centers through crystal deformation. Even though this type of coupling has been investigated intensively in the past, several inconsistencies exist in available literature, and no complete and consistent theoretical description has been given thus far. To clarify and resolve these issues, we here develop a complete and consistent formalism to describe the coupling between the NV spin degree of freedom and crystal deformation in terms of stress, defined in the crystal coordinate system XY Z, and strain, defined in the four individual NV reference frames. We find that the stress-based approach is straightforward, yields compact expressions for stress-induced level shifts and therefore constitutes the preferred approach to be used in future advances in the field. In contrast, the strain-based formalism is much more complicated and requires extra care when transforming into the employed NV reference frames. Furthermore, we illustrate how the developed formalism can be employed to extract values for the spin-stress and spin-strain coupling constants from data published by Teissier et al. 16 .

There are no bound oxygen isotopes past N = 16 while bound fluorine isotopes extend out to at least N = 22. Understanding the change in nuclear structure that underlies this difference has been the focus of considerable theoretical work. This change has been attributed to the spin-isospin component of the nucleon-nucleon force [1] which results in a larger energy gap between the ν(1s 1/2 ) and ν(0d 3/2 ) orbitals in oxygen isotopes [2]. At the same time, the gap between the ν(0d 3/2 ) orbital and the pf shell decreases as the number of protons increases from Z = 8 to Z = 14 [3]. While the anomaly in the location of the oxygen dripline is not reproduced by shell-model calculations based on microscopic two-nucleon forces, it was recently demonstrated that the inclusion of three-nucleon forces provides a microscopic explanation [4]. The smaller shell gap enhances the possibility for cross-shell excitations. The Monte Carlo shell model with SDPF-M effective interactions (MCSM), which includes cross-shell excitations [5,6], reproduces data in the region of the "island of inversion" [7]. This region of the nuclear chart includes neutron-rich Ne, Na, and Mg nuclei whose low-lying structure is dominated by neutron particle-hole excitations across the N = 20 shell gap ( [7,8] and references therein).Indications for cross-shell excitations have also been observed in neutron-rich fluorine isotopes [9]. While the first *

We demonstrate the use of shortcuts to adiabaticity protocols for initialisation, readout, and coherent control of dressed states generated by closed-contour, coherent driving of a single spin. Such dressed states have recently been shown to exhibit efficient coherence protection, beyond what their two-level counterparts can offer. Our state transfer protocols yield a transfer fidelity of ∼ 99.4(2) % while accelerating the transfer speed by a factor of 2.6 compared to the adiabatic approach. We show bi-directionality of the accelerated state transfer, which we employ for direct dressed state population readout after coherent manipulation in the dressed state manifold. Our results enable direct and efficient access to coherence-protected dressed states of individual spins and thereby offer attractive avenues for applications in quantum information processing or quantum sensing.