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Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration., Comment: 181 pages, 61 figures

We are interested in the opto-mechanical manipulation of nanodiamonds with a high concentration of SiV centers. Optical tweezers usually rely on the interaction of light and the ‘bulk’ polarizability of the nanoparticle itself. Here we exploit the polarizability of electronic resonances of optical centers embedded in the solid-state matrix to enhance the optical forces. This effect becomes particularly relevant for ensembles of active centers. The emitters being closely packed in a sub-wavelength volume, can act cooperatively, enhancing further the optical forces. This opens the possibility to apply the powerful toolbox of atomic physics for the quantum manipulation of ‘massive’ mesoscopic objects.

We propose to extend the search for new physics beyond Standard Model using optically trapped and laser cooled dielectric nanoparticles for the resonant detection of short-range forces and corrections to Newtonian gravity. © 2019 The Authors

We propose a small-scale spaceborne probe which uses laser-cooled optically-levitated nanoparticles to search for a variety of sources associated with high frequency cosmic events, through high-precision measurements and detection of gravitational waves at micron distances.

In this work, we investigate methods of fabricating a device for the optical actuation of nanoparticles. To create the microfluidic channel, we pursued three fabrication methods: SU-8 to molded polydimethylsiloxane soft lithography, laser etching of glass, and deep reactive ion etching of fused silica. We measured the surface roughness of the etched sidewalls, and the laser power transmission through each device. We then measured the radiation pressure on 0.5-µm particles in the best-performing fabricated device (etched fused silica) and in a square glass capillary.

We perform the experimental generation of pairs of photons on a solid-state rare-earth ion doped crystal of Eu 3p :Y 2 SiO 5 , by using a DLCZ-like protocol designed for inhomogeneously broadened media. The idea relies on the use of the atomic frequency comb technique, in order to rephase the atoms for the emission of the photons. A specificity of this protocol is its high temporal multimode capacity, as many pairs of photons can be emitted at different instants in time. A Cauchy-Schwarz inequality violation of 2.88>1 is witnessed, proving the non-classical correlations of the photon pairs that we produce. A detailed analysis of the source and detection imperfections is conducted, revealing ways of increasing the quality of the pairs that are produced.

The realization of quantum networks and quantum repeaters remains an outstanding challenge in quantum communication. These rely on the entanglement of remote matter systems, which in turn requires the creation of quantum correlations between a single photon and a matter system. A practical way to establish such correlations is via spontaneous Raman scattering in atomic ensembles, known as the Duan-Lukin-Cirac-Zoller (DLCZ) scheme. However, time multiplexing is inherently difficult using this method, which leads to low communication rates even in theory. Moreover, it is desirable to find solid-state ensembles where such matter-photon correlations could be generated. Here we demonstrate quantum correlations between a single photon and a spin excitation in up to 12 temporal modes, in a ^{151}Eu^{3+}-doped Y_{2}SiO_{5} crystal, using a novel DLCZ approach that is inherently multimode. After a storage time of 1 ms, the spin excitation is converted into a second photon. The quantum correlation of the generated photon pair is verified by violating a Cauchy-Schwarz inequality. Our results show that solid-state rare-earth-ion-doped crystals could be used to generate remote multimode entanglement, an important resource for future quantum networks.

We present a detailed study of the lifetime of optical spectral holes due to population storage in Zeeman sublevels of ${\mathrm{Nd}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$. The lifetime is measured as a function of magnetic field strength and orientation, temperature, and ${\mathrm{Nd}}^{3+}$ doping concentration. At the lowest temperature of 3 K we find a general trend where the lifetime is short at low field strengths, then increases to a maximum lifetime at a few hundred mT, and then finally decays rapidly for high field strengths. This behavior can be modeled with a relaxation rate dominated by ${\mathrm{Nd}}^{3+}\ensuremath{-}{\mathrm{Nd}}^{3+}$ cross relaxation at low fields and spin lattice relaxation at high magnetic fields. The maximum lifetime depends strongly on both the field strength and orientation, due to the competition between these processes and their different angular dependencies. The cross relaxation limits the maximum lifetime for concentrations as low as 30 ppm of ${\mathrm{Nd}}^{3+}$ ions. By decreasing the concentration to less than 1 ppm we could completely eliminate the cross relaxation, reaching a lifetime of 3.8 s at 3 K. At higher temperatures the spectral hole lifetime is limited by the magnetic-field-independent Raman and Orbach processes. In addition we show that the cross relaxation rate can be strongly reduced by creating spectrally large holes of the order of the optical inhomogeneous broadening. Our results are important for the development and design of new rare-earth-ion doped crystals for quantum information processing and narrow-band spectral filtering for biological tissue imaging.

We report on a direct measurement of the pairwise antisymmetric exchange interaction, known as the Dzyaloshinsky-Moriya interaction (DMI), in a Nd^{3+}-doped YVO_{4} crystal. To this end, we introduce a broadband electron spin resonance technique coupled with an optical detection scheme which selectively detects only one Nd^{3+}-Nd^{3+} pair. Using this technique we can fully measure the spin-spin coupling tensor, allowing us to experimentally determine both the strength and direction of the DMI vector. We believe that this ability to fully determine the interaction Hamiltonian is of interest for studying the numerous magnetic phenomena where the DMI interaction is of fundamental importance, including multiferroics. We also detect a singlet-triplet transition within the pair, with a highly suppressed magnetic-field dependence, which suggests that such systems could form singlet-triplet qubits with long coherence times for quantum information applications.

Long-distance quantum communication through optical fibers is currently limited to a few hundreds of kilometres due to fiber losses. Quantum repeaters could extend this limit to continental distances. Most approaches to quantum repeaters require highly multimode quantum memories in order to reach high communication rates. The atomic frequency comb memory scheme can in principle achieve high temporal multimode storage, without sacrificing memory efficiency. However, previous demonstrations have been hampered by the difficulty of creating high-resolution atomic combs, which reduces the efficiency for multimode storage. In this article we present a comb preparation method that allows one to increase the multimode capacity for a fixed memory bandwidth. We apply the method to a $^{151}$Eu$^{3+}$-doped Y$_2$SiO$_5$ crystal, in which we demonstrate storage of 100 modes for 51 $\mu$s using the AFC echo scheme (a delay-line memory), and storage of 50 modes for 0.541 ms using the AFC spin-wave memory (an on-demand memory). We also briefly discuss the ultimate multimode limit imposed by the optical decoherence rate, for a fixed memory bandwidth., Comment: 10 pages, 8 figures

Long-lived quantum memories are essential components of a long-standing goal of remote distribution of entanglement in quantum networks. These can be realized by storing the quantum states of light as single-spin excitations in atomic ensembles. However, spin states are often subjected to different dephasing processes that limit the storage time, which in principle could be overcome using spin-echo techniques. Theoretical studies have suggested this to be challenging due to unavoidable spontaneous emission noise in ensemble-based quantum memories. Here we demonstrate spin-echo manipulation of a mean spin excitation of 1 in a large solid-state ensemble, generated through storage of a weak optical pulse. After a storage time of about 1 ms we optically read out the spin excitation with a high signal-to-noise ratio. Our results pave the way for long-duration optical quantum storage using spin-echo techniques for any ensemble-based memory., Comment: 5 pages, 2 figures, 1 table

We report on the experimental demonstration of an optical spin-wave memory, based on the atomic frequency comb (AFC) scheme, where the storage efficiency is strongly enhanced by an optical cavity. The cavity is of low finesse, but operated in an impedance matching regime to achieve high absorption in our intrinsically low-absorbing Eu3+:Y2SiO5 crystal. For storage of optical pulses as an optical excitation (AFC echoes), we reach efficiencies of 53% and 28% for 2 and 10 microseconds delays, respectively. For a complete AFC spin-wave memory we reach an efficiency of 12%, including spin-wave dephasing, which is a 12-fold increase with respect to previous results in this material. This result is an important step towards the goal of making efficient and long-lived quantum memories based on spin waves, in the context of quantum repeaters and quantum networks.