Two-quantum magnetic resonance driven by a comb-like rf field.

We report a new method for excitation of magnetic resonance in an optically aligned atomic ensemble. It employs a comb-like rf field acting on the end sublevels of the =1 state separated by the doubled Zeeman frequency. This approach provides a resonance without substructures associated with the quadratic Zeeman shift.

Generation and manipulation of Schrödinger cat states in Rydberg atom arrays.

Quantum entanglement involving coherent superpositions of macroscopically distinct states is among the most striking features of quantum theory, but its realization is challenging because such states are extremely fragile. Using a programmable quantum simulator based on neutral atom arrays with interactions mediated by Rydberg states, we demonstrate the creation of "Schrödinger cat" states of the Greenberger-Horne-Zeilinger (GHZ) type with up to 20 qubits. Our approach is based on engineering the energy spectrum and using optimal control of the many-body system.

High-Fidelity Control and Entanglement of Rydberg-Atom Qubits.

Individual neutral atoms excited to Rydberg states are a promising platform for quantum simulation and quantum information processing. However, experimental progress to date has been limited by short coherence times and relatively low gate fidelities associated with such Rydberg excitations. We report progress towards high-fidelity quantum control of Rydberg-atom qubits.

Photon-mediated interactions between quantum emitters in a diamond nanocavity.

Photon-mediated interactions between quantum systems are essential for realizing quantum networks and scalable quantum information processing. We demonstrate such interactions between pairs of silicon-vacancy (SiV) color centers coupled to a diamond nanophotonic cavity. When the optical transitions of the two color centers are tuned into resonance, the coupling to the common cavity mode results in a coherent interaction between them, leading to spectrally resolved superradiant and subradiant states.

Probing many-body dynamics on a 51-atom quantum simulator.

Controllable, coherent many-body systems can provide insights into the fundamental properties of quantum matter, enable the realization of new quantum phases and could ultimately lead to computational systems that outperform existing computers based on classical approaches. Here we demonstrate a method for creating controlled many-body quantum matter that combines deterministically prepared, reconfigurable arrays of individually trapped cold atoms with strong, coherent interactions enabled by excitation to Rydberg states. We realize a programmable Ising-type quantum spin model with tunable interactions and system sizes of up to 51 qubits.

Quantum electronics. Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit.

Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films.

Indistinguishable photons from separated silicon-vacancy centers in diamond.

We demonstrate that silicon-vacancy (SiV) centers in diamond can be used to efficiently generate coherent optical photons with excellent spectral properties. We show that these features are due to the inversion symmetry associated with SiV centers. The generation of indistinguishable single photons from separated emitters at 5 K is demonstrated in a Hong-Ou-Mandel interference experiment.

Coherent optical transitions in implanted nitrogen vacancy centers.

We report the observation of stable optical transitions in nitrogen-vacancy (NV) centers created by ion implantation. Using a combination of high temperature annealing and subsequent surface treatment, we reproducibly create NV centers with zero-phonon lines (ZPL) exhibiting spectral diffusion that is close to the lifetime-limited optical line width. The residual spectral diffusion is further reduced by using resonant optical pumping to maintain the NV(-) charge state.

Coupling of NV centers to photonic crystal nanobeams in diamond.

The realization of efficient optical interfaces for solid-state atom-like systems is an important problem in quantum science with potential applications in quantum communications and quantum information processing. We describe and demonstrate a technique for coupling single nitrogen vacancy (NV) centers to suspended diamond photonic crystal cavities with quality factors up to 6000. Specifically, we present an enhancement of the NV center's zero-phonon line fluorescence by a factor of ~ 7 in low-temperature measurements.

Coupling a single trapped atom to a nanoscale optical cavity.

Hybrid quantum devices, in which dissimilar quantum systems are combined in order to attain qualities not available with either system alone, may enable far-reaching control in quantum measurement, sensing, and information processing. A paradigmatic example is trapped ultracold atoms, which offer excellent quantum coherent properties, coupled to nanoscale solid-state systems, which allow for strong interactions. We demonstrate a deterministic interface between a single trapped rubidium atom and a nanoscale photonic crystal cavity.

Coherence and Raman sideband cooling of a single atom in an optical tweezer.

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n(x)=n(y)=0.

Free-standing mechanical and photonic nanostructures in single-crystal diamond.

A variety of nanoscale photonic, mechanical, electronic, and optoelectronic devices require scalable thin film fabrication. Typically, the device layer is defined by thin film deposition on a substrate of a different material, and optical or electrical isolation is provided by the material properties of the substrate or by removal of the substrate. For a number of materials this planar approach is not feasible, and new fabrication techniques are required to realize complex nanoscale devices.

Quantum interference of single photons from remote nitrogen-vacancy centers in diamond.

We demonstrate quantum interference between indistinguishable photons emitted by two nitrogen-vacancy centers in distinct diamond samples separated by two meters. Macroscopic solid immersion lenses are used to enhance photon collection efficiency. Quantum interference is verified by measuring a value of the second-order cross-correlation function g((2))(0)=0.

Quantum entanglement between an optical photon and a solid-state spin qubit.

Quantum entanglement is among the most fascinating aspects of quantum theory. Entangled optical photons are now widely used for fundamental tests of quantum mechanics and applications such as quantum cryptography. Several recent experiments demonstrated entanglement of optical photons with trapped ions, atoms and atomic ensembles, which are then used to connect remote long-term memory nodes in distributed quantum networks.

Trapping and manipulation of isolated atoms using nanoscale plasmonic structures.

We propose and analyze a scheme to interface individual neutral atoms with nanoscale solid-state systems. The interface is enabled by optically trapping the atom via the strong near-field generated by a sharp metallic nanotip. We show that under realistic conditions, a neutral atom can be trapped with position uncertainties of just a few nanometers, and within tens of nanometers of other surfaces.

Repetitive readout of a single electronic spin via quantum logic with nuclear spin ancillae.

Robust measurement of single quantum bits plays a key role in the realization of quantum computation and communication as well as in quantum metrology and sensing. We have implemented a method for the improved readout of single electronic spin qubits in solid-state systems. The method makes use of quantum logic operations on a system consisting of a single electronic spin and several proximal nuclear spin ancillae in order to repetitively readout the state of the electronic spin.

Efficient all-optical switching using slow light within a hollow fiber.

We demonstrate a fiber-optical switch that is activated at tiny energies corresponding to a few hundred optical photons per pulse. This is achieved by simultaneously confining both photons and a small laser-cooled ensemble of atoms inside the microscopic hollow core of a single-mode photonic-crystal fiber and using quantum optical techniques for generating slow light propagation and large nonlinear interaction between light beams.

Nanoscale magnetic sensing with an individual electronic spin in diamond.

Detection of weak magnetic fields with nanoscale spatial resolution is an outstanding problem in the biological and physical sciences. For example, at a distance of 10 nm, the spin of a single electron produces a magnetic field of about 1 muT, and the corresponding field from a single proton is a few nanoteslas. A sensor able to detect such magnetic fields with nanometre spatial resolution would enable powerful applications, ranging from the detection of magnetic resonance signals from individual electron or nuclear spins in complex biological molecules to readout of classical or quantum bits of information encoded in an electron or nuclear spin memory.

Compact diode-laser based rubidium frequency reference.

The performance of a simple microwave frequency reference based on Raman scattering in an atomic vapor is examined. This reference has the potential to be compact, low-power, and insensitive to acceleration. Several design architectures have been evaluated with a table-top experiment in order to guide the future development of a compact system.

Observation of Ramsey fringes in an atomic cell with buffer gas.

Temporal Ramsey fringes that are due to light scattering by coherently prepared rubidium atoms diffusing through a cell containing neon as a buffer gas have been observed. The effect leads to increasing magneto-optical rotation of cw light polarization at weak magnetic fields.

Generation of single optical plasmons in metallic nanowires coupled to quantum dots.

Control over the interaction between single photons and individual optical emitters is an outstanding problem in quantum science and engineering. It is of interest for ultimate control over light quanta, as well as for potential applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits. Recently, substantial advances have been made towards these goals, based on modifying photon fields around an emitter using high-finesse optical cavities.

Quantum register based on individual electronic and nuclear spin qubits in diamond.

The key challenge in experimental quantum information science is to identify isolated quantum mechanical systems with long coherence times that can be manipulated and coupled together in a scalable fashion. We describe the coherent manipulation of an individual electron spin and nearby individual nuclear spins to create a controllable quantum register. Using optical and microwave radiation to control an electron spin associated with the nitrogen vacancy (NV) color center in diamond, we demonstrated robust initialization of electron and nuclear spin quantum bits (qubits) and transfer of arbitrary quantum states between them at room temperature.

Coherent dynamics of coupled electron and nuclear spin qubits in diamond.

Understanding and controlling the complex environment of solid-state quantum bits is a central challenge in spintronics and quantum information science. Coherent manipulation of an individual electron spin associated with a nitrogen-vacancy center in diamond was used to gain insight into its local environment. We show that this environment is effectively separated into a set of individual proximal 13C nuclear spins, which are coupled coherently to the electron spin, and the remainder of the 13C nuclear spins, which cause the loss of coherence.

Comparison of 87Rb N-resonances for D1 and D2 transitions.

We report an experimental comparison of three-photon-absorption resonances (N-resonances) for the D1 and D2 optical transitions of thermal (87)Rb vapor. We find that the D2 N-resonance has better contrast, a broader linewidth, and a more symmetric line shape than the D1 N-resonance. Taken together, these factors imply superior performance for frequency standards operating on alkali D2 N-resonances, in contrast with coherent population trapping resonances, for which the D2 transition provides poorer frequency standard performance than the D1 transition.

Experimental preparation of pure superposition states of atoms via elliptically polarized bichromatic radiation.

We propose a simple and effective way of creating pure dark superposition states. The generation of pure states is carried out by using bichromatic radiation with controllable polarization ellipticity. We experimentally confirm analytic formulas for polarization ellipticity to obtain m-m pure dark states in the system of Zeeman sublevels of alkali atoms.