A mechanically stable and tunable cryogenic Fabry-Pérot microcavity.

High-finesse, open-geometry microcavities have recently emerged as a versatile tool for enhancing interactions between photons and material systems with a range of applications in quantum optics and quantum information science. However, mechanical vibrations pose a considerable challenge to their operation within a closed-cycle cryostat, particularly when spatial tunability and free-space optical access are required. Here, we present the design and characterization of a system that can achieve ∼16 pm-rms passive mechanical stability between two high-finesse mirrors with 34% duty cycle while permitting both three-dimensional positioning of the cavity mode and free-space confocal imaging. The design relies on two cascaded vibration isolation stages connected by leaf springs that decouple axial and lateral motion and incorporates tuned-mass and magnetic damping. Furthermore, we present a technique for quantifying cavity length displacements similar to or larger than the cavity linewidth, allowing for the in situ measurement of vibrations with and without active feedback. Our results facilitate operation of a tunable, high-finesse cavity within a closed-cycle cryostat, representing an enabling technology for cavity coupling to a variety of solid-state systems.

Heralded entanglement between solid-state qubits separated by three metres.

Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin-photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks.

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. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond. Our experimental entanglement verification uses the quantum eraser technique, and demonstrates that a high degree of control over interactions between a solid-state qubit and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks.

Coherence of an optically illuminated single nuclear spin qubit.

We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt, Science 316, 1312 (2007)10.1126/science.1139831] when a proximal electronic spin associated with a nitrogen-vacancy (N-V) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.

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. Moreover, nuclear spin qubits could be well isolated from the electron spin, even during optical polarization and measurement of the electronic state. Finally, coherent interactions between individual nuclear spin qubits were observed and their excellent coherence properties were demonstrated. These registers can be used as a basis for scalable, optically coupled quantum information systems.

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. The proximal nuclear spins can be addressed and coupled individually because of quantum back-action from the electron, which modifies their energy levels and magnetic moments, effectively distinguishing them from the rest of the nuclei. These results open the door to coherent manipulation of individual isolated nuclear spins in a solid-state environment even at room temperature.

Fault-tolerant quantum communication based on solid-state photon emitters.

We describe a novel protocol for a quantum repeater that enables long-distance quantum communication through realistic, lossy photonic channels. Contrary to previous proposals, our protocol incorporates active purification of arbitrary errors at each step of the protocol using only two qubits at each repeater station. Because of these minimal physical requirements, the present protocol can be realized in simple physical systems such as solid-state single photon emitters. As an example, we show how nitrogen-vacancy color centers in diamond can be used to implement the protocol, using the nuclear and electronic spin to form the two qubits.

Shaping quantum pulses of light via coherent atomic memory.

We describe proof-of-principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatiotemporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and Electromagnetically Induced Transparency in an optically dense atomic medium. Using photon counting experiments, we observe Electromagnetically Induced Transparency based generation and shaping of few-photon sub-Poissonian light pulses.

Differential charge sensing and charge delocalization in a tunable double quantum dot.

We report measurements of a tunable double quantum dot, operating in the quantum regime, with integrated local charge sensors. The spatial resolution of the sensors allows the charge distribution within the double dot system to be resolved at fixed total charge. We use this readout scheme to investigate charge delocalization as a function of temperature and strength of tunnel coupling, demonstrating that local charge sensing can be used to accurately determine the interdot coupling in the absence of transport.

Managed Care College: a continuing education program for primary care clinicians.

This paper provides an overview of the Metro Medical Group Managed Care College--a new program of continuing medical education in primary care, created by the organization to improve the care it provides and demonstrate a new model that might serve as a prototype for other managed care organizations.

Multi-institutional drug-use evaluation of intraocular irrigating solutions.

A collaborative drug-use evaluation (DUE) of intraocular irrigating solutions (IOISs) at ophthalmic specialty hospitals nationwide is reported. Qualifying criteria for the use of an expensive fortified IOIS product were (1) the duration of surgery is more than 60 minutes, (2) the surgery is performed without a viscoelastic agent, (3) the patient's age is less than 50 years, (4) the patient has diabetes, and (5) the patient has evidence of compromised corneal endothelium. Surgical cases involving the use of IOISs were identified at each institution, and those cases involving fortified IOIS were reviewed for conformance with the criteria established. Of 23 institutions, 10 were able to perform the DUE. The review was concurrent at one institution and retrospective at the other nine. A case had to meet only one criterion to be considered in conformance. The cumulative mean rate of conformance with at least one criterion was 74%; the median conformance rate was 91%. The criteria that most frequently justified the use of fortified IOIS were surgical duration and nonuse of a viscoelastic material. Conformance with the DUE criteria varied with the institution, but valuable knowledge about the use of intraocular irrigating solutions was obtained by all.

Potential bacterial contamination in fluorescein-anesthetic solutions.

To determine the ability of fluorescein-anesthetic combination solutions and their applicators to regain sterility, we contaminated four commercially available fluorescein-anesthetic solutions and their dropper tips with inocula of either Pseudomonas species or Staphylococcus species. No organisms could be cultured from Fluress one minute after inoculation of the solution or five minutes after inoculation of the dropper tip. In contrast, organisms were cultured from the other fluorescein-anesthetic preparations for at least one hour after bacterial inoculation into the solution or onto the dropper tip. These differences in the ability of fluorescein-anesthetic solutions to regain sterility after bacterial contamination were statistically significant.

Renal and gastric hamartomas.

This report documents a patient with renal tumor which was originally diagnosed as "Wilms' tumor" and treated by irradiation and chemotherapy. Fifteen years later the patient was found to have gastric hamartomas. Reviews of the kidney tumor revealed it to be composed of morphologic features consistent with renal hamartoma rather than Wilms' tumor. We wish to report this extremely unusual association of renal and gastric hamartomas.