Passive Cooling of a Micromechanical Oscillator with a Resonant Electric Circuit

We cool the fundamental mode of a miniature cantilever by capacitively coupling it to a driven rf resonant circuit. Cooling results from the rf capacitive force, which is phase shifted relative to the cantilever motion. We demonstrate the technique by cooling a 7 kHz cantilever from room temperature to 45 K, obtaining reasonable agreement with a model for the cooling, damping, and frequency shift. Extending the method to higher frequencies in a cryogenic system could enable ground state cooling and may prove simpler than related optical experiments in a low temperature apparatus.Comment: 4 pages, 4 figures; minor changes to match published versio

Quantum information processing with trapped ions

Experiments directed towards the development of a quantum computer based on trapped atomic ions are described briefly. We discuss the implementation of single qubit operations and gates between qubits. A geometric phase gate between two ion qubits is described. Limitations of the trapped-ion method such as those caused by Stark shifts and spontaneous emission are addressed. Finally, we describe a strategy to realize a large-scale device.Comment: Article submitted by D. J. Wineland ([email protected]) for proceeding of the Discussion Meeting on Practical Realisations of Quantum Information Processing, held at the Royal Society, Nov. 13,14, 200

Manipulating a qubit through the backaction of sequential partial measurements and real-time feedback

Quantum measurements not only extract information from a system but also alter its state. Although the outcome of the measurement is probabilistic, the backaction imparted on the measured system is accurately described by quantum theory. Therefore, quantum measurements can be exploited for manipulating quantum systems without the need for control fields. We demonstrate measurement-only state manipulation on a nuclear spin qubit in diamond by adaptive partial measurements. We implement the partial measurement via tunable correlation with an electron ancilla qubit and subsequent ancilla readout. We vary the measurement strength to observe controlled wavefunction collapse and find post-selected quantum weak values. By combining a novel quantum non-demolition readout on the ancilla with real-time adaption of the measurement strength we realize steering of the nuclear spin to a target state by measurements alone. Besides being of fundamental interest, adaptive measurements can improve metrology applications and are key to measurement-based quantum computing.Comment: 6 pages, 4 figure

Designing spin-spin interactions with one and two dimensional ion crystals in planar micro traps

We discuss the experimental feasibility of quantum simulation with trapped ion crystals, using magnetic field gradients. We describe a micro structured planar ion trap, which contains a central wire loop generating a strong magnetic gradient of about 20 T/m in an ion crystal held about 160 \mu m above the surface. On the theoretical side, we extend a proposal about spin-spin interactions via magnetic gradient induced coupling (MAGIC) [Johanning, et al, J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 154009]. We describe aspects where planar ion traps promise novel physics: Spin-spin coupling strengths of transversal eigenmodes exhibit significant advantages over the coupling schemes in longitudinal direction that have been previously investigated. With a chip device and a magnetic field coil with small inductance, a resonant enhancement of magnetic spin forces through the application of alternating magnetic field gradients is proposed. Such resonantly enhanced spin-spin coupling may be used, for instance, to create Schr\"odinger cat states. Finally we investigate magnetic gradient interactions in two-dimensional ion crystals, and discuss frustration effects in such two-dimensional arrangements.Comment: 20 pages, 13 figure

On-ground performance tests of the SAX/PDS detector

The Phoswich Detection System (PDS) is one of the four narrow field experiments on board the SAX satellite. The PDS will be dedicated to deep temporal and spectral studies of celestial X-ray sources in the 15–300 keV energy band. It also includes a gamma-ray burst monitor. The PDS detector is composed of 4 actively shielded NaI(Tl)/CsI(Na) phoswich scintillators with a total geometric area of 795 cm2 and a field of view of 1:4 (FWHM). The performance of the detector, before its integration with its flight electronic, was tested using standard instrumentation. Here we present results of these tests. The measured energy resolution of the phoswich units is better than 15% at 60 keV, confirming the expectations. Also test results of the anticoincidence shield of CsI(Na) and collimator are discussed

Demonstration of integrated microscale optics in surface-electrode ion traps

In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion-photon entanglement. The expected size of future many-ion processors require scalable light collection systems. We report on the development and testing of a microfabricated surface-electrode ion trap with an integrated high numerical aperture (NA) micromirror for fluorescence collection. When coupled to a low NA lens, the optical system is inherently scalable to large arrays of mirrors in a single device. We demonstrate stable trapping and transport of 40Ca+ ions over a 0.63 NA micromirror and observe a factor of 1.9 enhancement in photon collection compared to the planar region of the trap.Comment: 15 pages, 8 figure

Sympathetic cooling of 9Be+^9Be^+ and 24Mg+^{24}Mg^+ for quantum logic

We demonstrate the cooling of a two species ion crystal consisting of one $^9Be^+$ and one $^{24}Mg^+$ ion. Since the respective cooling transitions of these two species are separated by more than 30 nm, laser manipulation of one ion has negligible effect on the other even when the ions are not individually addressed. As such this is a useful system for re-initializing the motional state in an ion trap quantum computer without affecting the qubit information. Additionally, we have found that the mass difference between ions enables a novel method for detecting and subsequently eliminating the effects of radio frequency (RF) micro-motion.Comment: Submitted to PR

Experimental limits on neutron disappearance into another braneworld

Recent theoretical works have shown that matter swapping between two parallel braneworlds could occur under the influence of magnetic vector potentials. In our visible world, galactic magnetism possibly produces a huge magnetic potential. As a consequence, this paper discusses the possibility to observe neutron disappearance into another braneworld in certain circumstances. The setup under consideration involves stored ultracold neutrons - in a vessel - which should exhibit a non-zero probability p to disappear into an invisible brane at each wall collision. An upper limit of p is assessed based on available experimental results. This value is then used to constrain the parameters of the theoretical model. Possible improvements of the experiments are discussed, including enhanced stimulated swapping by artificial means.Comment: 7 pages, 2 figures, 1 table. Published in Physics Letters