Single Trapped Atom Research Articles

Plasma‐electrified synthesis of atom‐efficient electrocatalysts for sustainable water catalysis and beyond

The downsizing of metal structures to the nano and atomic level, thereby creating nanoparticle catalysts (NPCs), sub‐nanometer cluster catalysts (SNCCs) or single atom catalysts (SACs), has gained significant interest. In particular, synthesizing these types of catalysts using low temperature plasma electrified methods is an emerging field which is highly applicable to electrochemical water splitting for the sustainable production of green hydrogen. Surface modification via plasma treatment provides a route for nanoparticle immobilization or single atom trapping which ensures high atom utilization during electrolysis reactions. Plasma can also be used to create NPCs, SNCCs and SACs from various precursors as well as modify their surface properties once formed which impacts significantly on the oxygen evolution reaction and hydrogen evolution reaction. Therefore, in this review we emphasize the role that low temperature plasma electrified synthetic strategies play in electrocatalyst development for water splitting reactions and explore the crucial relationship between the electronic and coordination environment of atom efficient catalysts and their resulting catalytic activity. We also discuss methods to characterize these types of catalysts and the possibility for scaling up this technology which will be required for commercial applications.

Controlling the interactions in a cold atom quantum impurity system

We implement an experimental architecture in which a single atom of K is trapped in an optical tweezer, and is immersed in a bath of Rb atoms at ultralow temperatures. In this regime, the motion of the single trapped atom is confined to the lowest quantum vibrational levels. This realizes an elementary and fully controllable quantum impurity system. For the trapping of the K atom, we use a species-selective dipole potential, that allows us to independently manipulate the quantum impurity and the bath. We concentrate on the characterization and control of the interactions between the two subsystems. To this end, we perform Feshbach spectroscopy, detecting several inter-dimensional confinement-induced Feshbach resonances for the KRb interspecies scattering length, that parametrizes the strength of the interactions. We compare our data to a theory for inter-dimensional scattering, finding good agreement. Notably, we also detect a series of p-wave resonances stemming from the underlying free-space s-wave interactions. We further determine how the resonances behave as the temperature of the bath and the dimensionality of the interactions change. Additionally, we are able to screen the quantum impurity from the bath by finely tuning the wavelength of the light that produces the optical tweezer, providing us with a new effective tool to control and minimize the interactions. Our results open a range of new possibilities in quantum simulations of quantum impurity models, quantum information, and quantum thermodynamics, where the interactions between a quantized system and the bath is a powerful yet largely underutilized resource.

Metasurface optical trap array for single atoms

Metasurfaces made of subwavelength silicon nanopillars provide unparalleled capacity to manipulate light, and have emerged as one of the leading platforms for developing integrated photonic devices. In this study, we report on a compact, passive approach based on planar metasurface optics to generate large optical trap arrays. The unique configuration is achieved with a meta-hologram to convert a single incident laser beam into an array of individual beams, followed up with a metalens to form multiple laser foci for single rubidium atom trapping. We experimentally demonstrate two-dimensional arrays of 5 × 5 and 25 × 25 at the wavelength of 830 nm, validating the capability and scalability of our metasurface design. Beam waists ∼1.5 µm, spacings (about 15 µm), and low trap depth variations (8%) of relevance to quantum control for an atomic array are achieved in a robust and efficient fashion. The presented work highlights a compact, stable, and scalable trap array platform well-suitable for Rydberg-state mediated quantum gate operations, which will further facilitate advances in neutral atom quantum computing.

Collisional dynamics of a few atom quantum system with tunable interaction

The advent of single-atom trapping in optical tweezers and experimental evolution in control, isolation, and manipulation of cold atoms allows us to manifest the few-body physics and its connection with the many-body systems. In cold atom experiments, the universality of few-body physics is majorly governed by the scattering length which makes it an important parameter in determining theoretically calculated loss rates. Here, we numerically study the 3-body collisional dynamics for Cesium atoms using the atom loss model described by Born-Markov approximation. Using the Cs atoms provides us the freedom to vary the scattering length, a, as a function of the magnetic field through Feshbach resonances. We investigate the three-, two-, and one-particle processes in the repulsive interactions regime at different values for a. We find that the probability of one atom remaining in the trap is maximum at B = 26 G corresponding to a = 402.382a 0 and has the highest value amongst the probability of zero-, two-, and three-particle remaining in the trap at same magnetic field after the collision. Our findings leads to high fidelity single atom tweezers which have direct application in creating defect free arrays for quantum information processing purposes.

Zero-threshold correlated-photon laser with a single trapped atom in a bimodal cavity

We demonstrate theoretically the feasibility of correlated entangled photon-pair generation with vanishing threshold in a bimodal cavity setup that uses a single V-type three level atom pumped by dual incoherent sources and driven by two coherent fields. The photon-pair is shown to be entangled only for low levels of the incoherent pumps and owes its origin solely to the coherent drives. Our results show that the dual incoherent pumping with no coherent drive can lead to amplification of the cavity fields with strong inter-mode antibunching but no entanglement. We analyse our results in terms of an interplay between coherent and incoherent processes involving cavity-dressed states. Both the inter- and intra-mode Hanbury–Brown–Twiss (HBT) functions exhibit temporal oscillations in the strong-coupling cavity QED regime. Our theoretical scheme for the generation of nonclassical and entangled photon pairs may find interesting applications in quantum metrology and quantum information science.

Competitive Trapping of Single Atoms onto a Metal Carbide Surface.

Controlling atomic adjustment of single-atom catalysts (SACs) can directly change its local configuration, regulate the energy barrier of intermediates, and further optimize reaction pathways. Herein, we report an atom manipulating process to synthesize Ni atoms stabilized on vanadium carbide (NiSA-VC) through a nanofiber-medium thermodynamically driven atomic migration strategy. Experimental and theoretical results systematically reveal the tunable migration pathway of Ni atom from Ni nanoparticles to neighboring N-doped carbon (NC) and finally to metal carbide that was obtained by regulating the competitive adsorption energies between VC and NC for capturing Ni atoms. For CO2-to-CO electroreduction, NiSA-VC exhibits an industrial current density of -180 mA cm-2 at -1.0 V vs reversible hydrogen electrode and the highest Faradaic efficiency for CO production (FECO) of 96.8% at -0.4 V vs RHE in a flow cell. Significant electron transfers occurring in NiSA-VC structures contribute to the activation of CO2, facilitate the reaction free energy, regulate *CO desorption as the rate-determining step, and promote the activity and selectivity. This study provides an understanding on how to design powerful SACs for electrocatalysis.

Interaction of twisted light with a trapped atom: Interplay between electronic and motional degrees of freedom

We present a theoretical study of nondipole excitation of a single trapped atom by twisted light. Special emphasis is placed on effects that arise from the interplay between internal (electronic) and vibrational (center-of-mass) degrees of freedom of an atom. In order to provide a fully quantum mechanical understanding of the excitation, we used the density-matrix approach based on the Liouville--von Neumann equation. The developed theory has been applied to the particular case of the $4s\phantom{\rule{0.16em}{0ex}}^{2}S_{1/2}\ensuremath{\rightarrow}3d\phantom{\rule{0.16em}{0ex}}^{2}D_{5/2}$ electric quadrupole ($E2$) transition in a $^{40}\mathrm{Ca}^{+}$ ion induced by Laguerre-Gaussian modes. It was found that the Rabi oscillations can show unconventional anharmonic behavior that is attributed to the strong coupling between vibrational levels of the trap. This effect is accompanied by the transfer of angular momentum to the center-of-mass motion and becomes most pronounced when the Rabi frequency is comparable to the trapping frequency.

Quantum jump spectroscopy of a single neutral atom for precise subwavelength intensity measurements

A single trapped neutral atom is used for precise subwavelength intensity measurements. Quantum jumps from a dark to a bright atomic state are used to boost signal-to-noise and avoid systematic errors.

Proposal for low-power atom trapping on a GaN-on-sapphire chip

The hybrid photon-atom integrated circuits, which include photonic microcavities and trapped single neutral atom in their evanescent field, are of great potential for quantum information processing. In this platform, the atoms provide the single-photon nonlinearity and long-lived memory, which are complementary to the excellent passive photonics devices in conventional quantum photonic circuits. In this work, we propose a stable platform for realizing the hybrid photon-atom circuits based on an unsuspended photonic chip. By introducing high-order modes in the microring, a feasible evanescent-field trap potential well $\sim0.3\,\mathrm{mK}$ could be obtained by only $10\,\mathrm{mW}$-level power in the cavity, compared with $100\,\mathrm{mW}$-level power required in the scheme based on fundamental modes. Based on our scheme, stable single atom trapping with relatively low laser power is feasible for future studies on high-fidelity quantum gates, single-photon sources, as well as many-body quantum physics based on a controllable atom array in a microcavity.

Microscopic 3D printed optical tweezers for atomic quantum technology

Trapping of single ultracold atoms is an important tool for applications ranging from quantum computation and communication to sensing. However, most experimental setups, while very precise and versatile, can only be operated in specialized laboratory environments due to their large size, complexity and high cost. Here, we introduce a new trapping concept for ultracold atoms in optical tweezers based on micrometer-scale lenses that are 3D printed onto the tip of standard optical fibers. The unique properties of these lenses make them suitable for both trapping individual atoms and capturing their fluorescence with high efficiency. In an exploratory experiment, we have established the vacuum compatibility and robustness of the structures, and successfully formed a magneto-optical trap for ultracold atoms in their immediate vicinity. This makes them promising components for portable atomic quantum devices.

Multigrating design for integrated single-atom trapping, manipulation, and readout

An on-chip multi-grating device is proposed to interface single-atoms and integrated photonic circuits, by guiding and focusing lasers to the area with ~10um above the chip for trapping, state manipulation, and readout of single Rubidium atoms. For the optical dipole trap, two 850 nm laser beams are diffracted and overlapped to form a lattice of single-atom dipole trap, with the diameter of optical dipole trap around 2.7um. Similar gratings are designed for guiding 780 nm probe laser to excite and also collect the fluorescence of 87Rb atoms. Such a device provides a compact solution for future applications of single atoms, including the single photon source, single-atom quantum register, and sensor.

Manipulating and measuring single atoms in the Maltese cross geometry.

Background: Optical microtraps at the focus of high numerical aperture (high-NA) imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms for quantum technology and studies of optical physics associated with super- and sub-radiant states. The recently developed "Maltese cross" geometry (MCG) atom trap uses four in-vacuum lenses to achieve four-directional high-NA optical coupling to single trapped atoms and small atomic arrays. This article presents the first extensive characterisation of atomic behaviour in a MCG atom trap. Methods: We employ a MCG system optimised for high coupling efficiency and characterise the resulting properties of the trap and trapped atoms. Using current best practices, we measure occupancy, loading rate, lifetime, temperature, fluorescence anti-bunching and trap frequencies. We also use the four-directional access to implement a new method to map the spatial distribution of collection efficiency from high-NA optics: we use the two on-trap-axis lenses to produce a 1D optical lattice, the sites of which are stochastically filled and emptied by the trap loading process. The two off-trap-axis lenses are used for imaging and single-mode collection. Correlations of single-mode and imaging fluorescence signals are then used to map the single-mode collection efficiency. Results:We observe trap characteristics comparable to what has been reported for single-atom traps with one- or two-lens optical systems. The collection efficiency distribution in the axial and transverse directions is directly observed to be in agreement with expected collection efficiency distribution from Gaussian beam optics. Conclusions: The multi-directional high-NA access provided by the Maltese cross geometry enables complex manipulations and measurements not possible in geometries with fewer directions of access, and can be achieved while preserving other trap characteristics such as lifetime, temperature, and trap size.

Trapping a single atom in the evanescent field of a WGM-resonator

We demonstrate the trapping of single atoms in the evanescent field of a whispering-gallery-mode (WGM) resonator with a standing wave optical dipole trap. We present our progress towards an improved trap loading scheme.

Engineering catalyst supports to stabilize PdOx two-dimensional rafts for water-tolerant methane oxidation

The treatment of emissions from natural gas engines is an important area of research since methane is a potent greenhouse gas. The benchmark catalysts, based on Pd, still face challenges such as water poisoning and long-term stability. Here we report an approach for catalyst synthesis that relies on the trapping of metal single atoms on the support surface, in thermally stable form, to modify the nature of further deposited metal/metal oxide. By anchoring Pt ions on a catalyst support we can tailor the morphology of the deposited phase. In particular, two-dimensional (2D) rafts of PdOx are formed, resulting in higher reaction rates and improved water tolerance during methane oxidation. The results show that modifying the support by trapping single atoms could provide an important addition to the toolkit of catalyst designers for controlling the nucleation and growth of metal and metal oxide clusters in heterogeneous catalysts.

Single Atoms with 6000-Second Trapping Lifetimes in Optical-Tweezer Arrays at Cryogenic Temperatures

We report on the trapping of single Rb atoms in tunable arrays of optical tweezers in a cryogenic environment at $\sim 4$ K. We describe the design and construction of the experimental apparatus, based on a custom-made, UHV compatible, closed-cycle cryostat with optical access. We demonstrate the trapping of single atoms in cryogenic arrays of optical tweezers, with lifetimes in excess of $\sim6000$ s, despite the fact that the vacuum system has not been baked out. These results open the way to large arrays of single atoms with extended coherence, for applications in large-scale quantum simulation of many-body systems, and more generally in quantum science and technology.

Manipulating and measuring single atoms in the Maltese cross geometry

Background: Optical microtraps at the focus of high numerical aperture (high-NA) imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms for quantum technology and studies of optical physics associated with super- and sub-radiant states. The recently developed “Maltese cross” geometry (MCG) atom trap uses four in-vacuum lenses to achieve four-directional high-NA optical coupling to single trapped atoms and small atomic arrays. This article presents the first extensive characterisation of atomic behaviour in a MCG atom trap. Methods: We employ a MCG system optimised for high coupling efficiency and characterise the resulting properties of the trap and trapped atoms. Using current best practices, we measure occupancy, loading rate, lifetime, temperature, fluorescence anti-bunching and trap frequencies. We also use the four-directional access to implement a new method to map the spatial distribution of collection efficiency from high-NA optics: we use the two on-trap-axis lenses to produce a 1D optical lattice, the sites of which are stochastically filled and emptied by the trap loading process. The two off-trap-axis lenses are used for imaging and single-mode collection. Correlations of single-mode and imaging fluorescence signals are then used to map the single-mode collection efficiency. Results: We observe trap characteristics comparable to what has been reported for single-atom traps with one- or two-lens optical systems. The collection efficiency distribution in the axial and transverse directions is directly observed to be in agreement with expected collection efficiency distribution from Gaussian beam optics. Conclusions: The multi-directional high-NA access provided by the Maltese cross geometry enables complex manipulations and measurements not possible in geometries with fewer directions of access, and can be achieved while preserving other trap characteristics such as lifetime, temperature, and trap size.

Trapping, detection and manipulation of single Rb atoms in an optical dipole trap using a long-focus objective lens

Single alkali-metal atoms in arrays of optical dipole traps represent a quantum register that can be used for quantum computation and simulation based on short-term Rydberg excitations, which switch the interactions between qubits. To load single atoms into optical dipole traps and then detect them by resonance fluorescence, lenses with a large numerical aperture (NA > 0.5) inside a vacuum chamber and expensive EMCCD cameras are commonly used. We present our recent experimental results on demonstrating the trapping of single 87Rb atoms using a long-focus objective lens with a low numerical aperture (NA = 0.172) placed outside the vacuum chamber, and detecting single atoms with a low-cost sCMOS camera. We also present our current results on implementing a single-qubit gate based on optical pumping and subsequent microwave transition between two hyperfine sublevels of a single 87Rb atom with fidelity near 95%.

Photon-level broadband spectroscopy and interferometry with two frequency combs

We probe complex optical spectra at high resolution over a broad span in almost complete darkness. Using a single photon-counting detector at light power levels that are a billion times weaker than commonly employed, we observe interferences in the counting statistics with two separate mode-locked femtosecond lasers of slightly different repetition frequencies, each emitting a comb of evenly spaced spectral lines over a wide spectral span. Unique advantages of the emerging technique of dual-comb spectroscopy, such as multiplex data acquisition with many comb lines, potential very high resolution, and calibration of the frequency scale with an atomic clock, can thus be maintained for scenarios where only few detectable photons can be expected. Prospects include spectroscopy of weak scattered light over long distances, fluorescence spectroscopy of single trapped atoms or molecules, or studies in the extreme-ultraviolet or even soft-X-ray region with comb sources of low photon yield. Our approach defies intuitive interpretations in a picture of photons that exist before detection.

Reduction of laser intensity noise over 1 MHz band for single atom trapping.

We reduce the intensity noise of laser light by using an electro-optic modulator and acousto-optic modulator in series. The electro-optic modulator reduces noise at high frequency (10 kHz to 1 MHz), while the acousto-optic modulator sets the average power of the light and reduces noise at low frequency (up to 10 kHz). The light is then used to trap single sodium atoms in an optical tweezer, where the lifetime of the atoms is limited by parametric heating due to laser noise at twice the trapping frequency. With our noise eater, the noise is reduced by up to 15 dB at these frequencies and the lifetime of the atom in the optical tweezer is increased by an order of magnitude to around 6 seconds. Our technique is general and acts directly on the laser beam, expanding laser options for sensitive optical trapping applications.

Trapping and detection of single rubidium atoms in an optical dipole trap using a long-focus objective lens

The trapping of single atoms in optical dipole traps is widely used in experiments on the implementation of quantum processors based on neutral atoms, and studying interatomic interactions. Typically, such experiments employ lenses with a large numerical aperture (NA > 0.5), highly sensitive EMCCD cameras, or photon counters. In this work, we demonstrate trapping and detection of single rubidium atoms using a long-focus objective lens with a numerical aperture NA = 0.172 and a FLir Tau CNV sCMOS camera.