Trapping and optically interfacing laser-cooled neutral atoms are essential requirements for their use in advanced quantum technologies. Here we simultaneously realize both of these tasks with cesium atoms interacting with a multicolor evanescent field surrounding an optical nanofiber. The atoms are localized in a one-dimensional optical lattice about 200 nm above the nanofiber surface and can be efficiently interrogated with a resonant light field sent through the nanofiber. Our technique opens the route towards the direct integration of laser-cooled atomic ensembles within fiber networks, an important prerequisite for large scale quantum communication schemes. Moreover, it is ideally suited to the realization of hybrid quantum systems that combine atoms with, e.g., solid state quantum devices.

We report the experimental realization of a single-atom heat engine. An ion is confined in a linear Paul trap with tapered geometry and driven thermally by coupling it alternately to hot and cold reservoirs. The output power of the engine is used to drive a harmonic oscillation. From direct measurements of the ion dynamics, we determine the thermodynamic cycles for various temperature differences of the reservoirs. We use these cycles to evaluate power P and efficiency η of the engine, obtaining up to P = 342 yJ and η = 2.8 , consistent with analytical estimations. Our results demonstrate that thermal machines can be reduced to the ultimate limit of single atoms.Heat engines have played a central role in our modern society since the industrial revolution. Converting thermal energy into mechanical work, they are ubiquitously employed to generate motion, from cars to airplanes [1]. The working fluid of a macroscopic engine typically contains of the order of 10 24 particles. In the last decade, dramatic experimental progress has lead to the miniaturization of thermal machines down to the microscale, using microelectromechanical [2], piezoresistive [3] and cold atom [4] systems, as well as single colloidal particles [5,6] and single molecules [7]. In his 1959 talk "There is plenty of room at the bottom", Richard Feynman already envisioned tiny motors working at the atomic level [8]. However, to date no such device has been built.Here we report the realization of a single-atom heat engine whose working agent is an ion, held within a modified linear Paul trap. We use laser cooling and electric field noise to engineer cold and hot reservoirs. We further employ fast thermometry methods to determine the temperature of the ion [9]. The thermodynamic cycle of the engine is established for various temperature differences of the reservoirs, from which we deduce work and heat, and thus power output and efficiency. We additionally show that the work produced by the engine can be effectively stored and used to drive an oscillator against friction. Our device demonstrates the working principles of a thermodynamic heat engine with a working agent reduced to the ultimate single particle limit, thus fulfilling Feynman's dream.Trapped ions offer an exceptional degree of preparation, control and measurement of their parameters, allowing for ground state cooling [10] and coupling to engineered reservoirs [11]. Owing to their unique properties, they have recently become invaluable tools for the investigation of quantum thermodynamics [12][13][14][15][16][17]. They additionally provide an ideal setup to operate and characterize a single particle heat engine.In our experiment, a single 40 Ca + ion is trapped in a linear Paul trap with a funnel-shaped electrode geometry, as shown in Fig. 1a [15]. The electrodes are driven symmetrically at a radio-frequency voltage of 830 V pp at 21 MHz, resulting in a tapered harmonic pseudopotential [10] of the form U = (m/2) i ω 2 i i 2 , where m is the atomic mass and i ∈ {x, y} denote the trap axes as...

We realize fast transport of ions in a segmented micro-structured Paul trap. The ion is shuttled over a distance of more than 10 4 times its groundstate wavefunction size during only 5 motional cycles of the trap (280 µm in 3.6 µs). Starting from a ground-state-cooled ion, we find an optimized transport such that the energy increase is as low as 0.10±0.01 motional quanta. In addition, we demonstrate that quantum information stored in a spin-motion entangled state is preserved throughout the transport. Shuttling operations are concatenated, as a proof-of-principle for the shuttling-based architecture to scalable ion trap quantum computing. . Scalable information processing in a multiplexed ion trap can be accomplished by having fixed processing sites where logic operations are performed, and ion qubits will be moved in and out of these regions by shuttling operations. The duration of such shuttling has to be much faster than the relevant decoherence times [4]. Furthermore, it is desirable to reduce the total time consumption of all relevant operations, where shuttling will contribute a considerable amount [5], and aim for the performance of the naturally fast solid state architectures [6]. So far, ion shuttling in a multiplexed trap has been demonstrated together with additional sympathetic cooling [7], and in the adiabatic regime, where the transient displacement of the ion is smaller than the size of the its wavepacket [8,9]. Transport of neutral atoms have also been performed using magnetic [10] or optical [11] techniques.Because quantum gate operations require ions close to the motional ground state and fast transport inherently creates motional excitation, the challenge is to develop transport protocols that guarantee sufficiency small energy transfer. In this work we demonstrate shuttling operations that are highly non-adiabatic while the final state of the ion is close to the motional groundstate. We also show that quantum information stored in both the motional and the spin degree of freedom is preserved through the shuttling.During a shuttling operation, the ion motion in the harmonic trapping potential is excited when the acceleration is sufficiently strong. This motional excitation is a harmonic oscillation, characterized by a well defined phase, thus allowing it to be canceled out by proper management of the forces involved during or after the transport. We experimentally demonstrate two methods of canceling the acquired motional excitation. One method uses two shuttles, where the transport to the destination generates the same net momentum transfer as the transport back, but is applied 180 • out of phase with respect to the secular oscillation of the ion (Fig. 1b). We refer to this as the pairwise energy-neutral transport. For the second scheme, the self-neutral transport we apply a sharp counter-"kick" to the ion at the end of a single transport operation, stopping its motion (Fig. 1c). This case of single-sided transport allows even faster shuttling and can be sequentially repeated since it is ener...

Traversal of a symmetry-breaking phase transition at finite rates can lead to causally separated regions with incompatible symmetries and the formation of defects at their boundaries, which has a crucial role in quantum and statistical mechanics, cosmology and condensed matter physics. This mechanism is conjectured to follow universal scaling laws prescribed by the Kibble-Zurek mechanism. Here we determine the scaling law for defect formation in a crystal of 16 laser-cooled trapped ions, which are conducive to the precise control of structural phases and the detection of defects. The experiment reveals an exponential scaling of defect formation g b , where g is the rate of traversal of the critical point and b ¼ 2.68 ± 0.06. This supports the prediction of b ¼ 8/3E2.67 for finite inhomogeneous systems. Our result demonstrates that the scaling laws also apply in the mesoscopic regime and emphasizes the potential for further tests of non-equilibrium thermodynamics with ion crystals.

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We dispersively interface an ensemble of one thousand atoms trapped in the evanescent field surrounding a tapered optical nanofiber. This method relies on the azimuthally-asymmetric coupling of the ensemble with the evanescent field of an off-resonant probe beam, transmitted through the nanofiber. The resulting birefringence and dispersion are significant; we observe a phase shift per atom of ∼ 1 mrad at a detuning of six times the natural linewidth, corresponding to an effective resonant optical density per atom of 0.027. Moreover, we utilize this strong dispersion to nondestructively determine the number of atoms.PACS numbers: 42.50. Ct, 37.10.Gh, 37.10.Jk We have recently demonstrated a new technique for trapping and optically interfacing cold atoms [1]. Our method employs one-dimensional arrays of laser-cooled atoms trapped in a two-color evanescent field surrounding an optical nanofiber. The resulting atomic ensemble is both well-isolated from perturbations by the environment and efficiently coupled to a fiber-guided probe field. This makes our system a prime candidate for interfacing and manipulating trapped atoms with light.In [1], the detection of cesium atoms was achieved by monitoring the transmission of resonant probe light through the nanofiber. This probe light couples efficiently to the atoms via its evanescent field resulting in an absorbance per atom of the order of one percent. This strong absorbance also implies that there is a significant phase shift of the probe light in the dispersive regime. In this paper, we present experimental evidence of this phase shift and show that it leads to a frequencydependent birefringence that acts on the polarization state of the probe light propagating through the fiber.Being based on dispersive detection, our method has significant advantages over absorption or fluorescencebased techniques [2]. As an example, its signal-to-noise ratio is superior in the case of high optical depth when assuming shot-noise-limited detection [3]. Conceptually, it is similar to other dispersive detection schemes for atoms and molecules such as interferometry [4,5], frequency modulation spectroscopy [6], or phase-contrast imaging [7].In all these approaches, the phase shift induced by the atomic medium on the probe beam is compared to the phase of a reference beam via interference. In the case of atoms trapped using a nanofiber, this can be accomplished by interfering two orthogonal polarization modes, which couple unequally to the atomic ensemble. The polarization state of the output light thus enables one to infer the phase shift caused by the atoms. Figure 1 shows a schematic of the experimental setup. The atoms are trapped in two one-dimensional arrays FIG. 1. Schematic of the setup: An off-resonant laser beam is coupled into the nanofiber to probe the cesium atoms, which are trapped in the evanescent field of the nanofiber forming two one-dimensional arrays above and below the fiber (zoomed inset). A Stokes measurement is performed on the outgoing probe beam using a quart...

We realize a single particle microscope by using deterministically extracted laser-cooled ^{40}Ca^{+} ions from a Paul trap as probe particles for transmission imaging. We demonstrate focusing of the ions to a spot size of 5.8±1.0  nm and a minimum two-sample deviation of the beam position of 1.5 nm in the focal plane. The deterministic source, even when used in combination with an imperfect detector, gives rise to a fivefold increase in the signal-to-noise ratio as compared with conventional Poissonian sources. Gating of the detector signal by the extraction event suppresses dark counts by 6 orders of magnitude. We implement a Bayes experimental design approach to microscopy in order to maximize the gain in spatial information. We demonstrate this method by determining the position of a 1  μm circular hole structure to a precision of 2.7 nm using only 579 probe particles.

Single dopant atoms or dopant-related defect centers in a solid state matrix provide an attractive platform for quantum simulation of topological states [1], for quantum computing and communication, due to their potential to realize a scalable architecture compatible with electronic and photonic integrated circuits [2][3][4][5][6][7]. The production of such quantum devices calls for deterministic single atom doping techniques because conventional stochastic doping techniques are cannot deliver appropriate architectures. Here, we present the fabrication of arrays of praseodymium color centers in YAG substrates, using a deterministic source of single laser-cooled Pr + ions. The beam of single Pr + ions is extracted from a Paul trap and focused down to 30(9) nm. Using a confocal microscope we determine a conversion yield into active color centers up to 50% and realizing a placement accuracy of better than 50 nm. PACS numbers:Deterministic doping methods at the nm-scale provide a route towards scalable quantum information processing in solid state systems. Prominent examples of atomic systems in solid state hosts for quantum computing are single phosphorus atoms in silicon [8,9] and spin correlated pairs of such donors [10,11] which have led to studies of the scalability of large arrays of coupled donors [8]. Alternatively, single color centers [12] and the growing variety of single rare-earth ions (REI) doped into crystalline hosts have also been employed [2,3,[13][14][15][16]. Driven by proposed quantum applications, the need to deterministically place single dopants into nanostructured devices has led to the development of various techniques related to the silicon material system [17,18]. Crystalline hosts of color centers and REI, however, typically exhibit poor electronic properties, which inhibits single ion detection via active substrates [17] and therefore an alternative technique for deterministic implantation of dopants is required. Here, we present an inherently deterministic method for single ion implantation based on a segmented Paul trap which allows for implantation in any solid state material with a broad range of implantation energies.For characterizing the implantation method, we use single praseodymium ion detection in yttrium aluminum garnet (YAG) crystals based on upconversion microscopy. This detection scheme requires implanted praseodymium ions to arrange in the proper lattice position and reach the Pr 3+ charge state through a suitable annealing and activation procedure. An accurate determination of the ratio of detected ions to implanted ions, commonly referred to as implantation yield, has been performed for the first time at the level of single ions and will further foster the optimization of annealing procedures. In comparison to previous implantation-based nitrogen and silicon vacancy color center generation experiments [19], we achieve more than 20 times higher yield for the implantation of Pr + in YAG, even at much lower implantation energies with correspondingly smaller straggling-rela...