: Physics Articles
Editorial: Here we go...After almost three decades of preparation, CERN's Large Hadron Collider is turning on. Nature Physics, vol. 4 #8, pp581-581 |
News and Views: Spin ratchets: A one-way street for spin currentA way to generate and control spin currents without magnetic fields or magnetic materials may be possible using dissipative quantum ratchets in the presence of spin–orbit coupling. Nature Physics, vol. 4 #8, pp587-588 |
News and Views: Superconducting qubits: Atomic physics with a circuitInspired by ideas and techniques for cooling atomic gases, an experiment demonstrates how the temperature of micrometre-scale electronic devices can be lowered using solid-state quantum circuits. Nature Physics, vol. 4 #8, pp589-590 |
News and Views: Quantum electronics: Hybrid electron controlThe ability to change the degree of hybridization of a donor electron between the coulombic potential of its donor atom and that of a nearby quantum well in a silicon transistor has now been achieved. This is a promising step in the development of atomic-scale quantum control. Nature Physics, vol. 4 #8, pp590-591 |
News and Views: Bose–Hubbard optical lattice: Peak on a peakWhen is a condensate really a condensate? Calculations reveal that a 'peak on a peak' structure should be considered the true signature of the emergence of a Bose condensate in a Bose–Hubbard optical lattice. Nature Physics, vol. 4 #8, pp592-593 |
Letter: Superconductivity and quantum criticality in the heavy-fermion system β-YbAlB4A long-sought ytterbium-based heavy-fermion superconductor—a hole analogue of the cerium-based systems—has been found. Moreover, there is evidence for a quantum critical point at ambient conditions and without chemical doping. Nature Physics, vol. 4 #8, pp603-607 |
Letter: Pairing fluctuations in the pseudogap state of copper-oxide superconductors probed by the Josephson effectThe pseudogap state in the high-temperature superconductors may be either a precursor state to superconductivity or a competing state. A direct probe of the Cooper pairs can address this conundrum. Nature Physics, vol. 4 #8, pp608-611 |
Letter: Sisyphus cooling and amplification by a superconducting qubitA superconducting qubit—a mesoscopic structure that behaves like a quantum two-level system—has been used to change the temperature of a resonant circuit, in close analogy to the so-called Sisyphus cooling and amplification protocols used in laser cooling of atoms. Nature Physics, vol. 4 #8, pp612-616 |
Letter: Sharp peaks in the momentum distribution of bosons in optical lattices in the normal stateCold atoms in optical lattices provide a unique laboratory for investigating quantum phase transitions between strongly correlated superfluid and Mott insulator phases. One of the major bottlenecks in the analysis of experiments is a clear set of criteria for identifying the superfluid phase. A ‘sharp’ interference pattern in time-of-flight experiments has been widely adopted as a signature of superfluidity. Here, we show that sharp peaks are not a reliable diagnostic of superfluidity. Using large-scale quantum Monte Carlo simulations of the Bose–Hubbard model in three dimensions with up to N=1.4×104 particles, we calculate the momentum distribution n(k) as a function of temperature T and t/U, the ratio of hopping to the onsite repulsion. We find that even above the transition temperature Tc where both superfluid density and condensate fraction vanish, the interference pattern can nevertheless have sharp peaks riding over a broad background. We identify the true signature of the superfluid and give a deeper understanding of why such sharp peaks appear in the normal state. Nature Physics, vol. 4 #8, pp617-621 |
Letter: Efficient state transfer in an ultracold dense gas of heteronuclear moleculesPolar molecules have bright prospects for novel quantum gases with long-range and anisotropic interactions, and could find uses in quantum information science and in precision measurements. However, high-density clouds of ultracold polar molecules have so far not been produced. Here, we report a key step towards this goal. We start from an ultracold dense gas of loosely bound 40K87Rb Feshbach molecules with typical binding energies of a few hundred kilohertz, and coherently transfer these molecules in a single transfer step into a vibrational level of the ground-state molecular potential bound by more than 10 GHz. Starting with a single initial state prepared with Feshbach association, we achieve a transfer efficiency of 84%. Given favourable Franck–Condon factors, the presented technique can be extended to access much more deeply bound vibrational levels and those exhibiting a significant dipole moment. Nature Physics, vol. 4 #8, pp622-626 |
Letter: Giant phonon-induced conductance in scanning tunnelling spectroscopy of gate-tunable grapheneScanning tunnelling spectra of a graphene field-effect transistor reveal an unexpected tenfold increase in conductance as a result of phonon-mediated inelastic tunnelling. Nature Physics, vol. 4 #8, pp627-630 |
Letter: Coherent dynamics of plasma mirrorsCoherent ultrashort X-ray pulses provide new ways to probe matter and its ultrafast dynamics. One of the promising paths to generate these pulses consists of using a nonlinear interaction with a system to strongly and periodically distort the waveform of intense laser fields, and thus produce high-order harmonics. Such distortions have so far been induced by using the nonlinear polarizability of atoms, leading to the production of attosecond light bursts, short enough to study the dynamics of electrons in matter. Shorter and more intense attosecond pulses, together with higher harmonic orders, are expected by reflecting ultraintense laser pulses on a plasma mirror—a dense (≈1023 electrons cm−3) plasma with a steep interface. However, short-wavelength-light sources produced by such plasmas are known to generally be incoherent. In contrast, we demonstrate that like in usual low-intensity reflection, the coherence of the light wave is preserved during harmonic generation on plasma mirrors. We then exploit this coherence for interferometric measurements and thus carry out a first study of the laser-driven coherent dynamics of the plasma electrons. Nature Physics, vol. 4 #8, pp631-634 |
Letter: An off-board quantum point contact as a sensitive detector of cantilever motionRecent advances in the fabrication of microelectromechanical systems and their evolution into nanoelectromechanical systems have enabled researchers to measure extremely small forces, masses and displacements. In particular, researchers have developed position transducers with resolution approaching the uncertainty limit set by quantum mechanics. The achievement of such resolution has implications not only for the detection of quantum behaviour in mechanical systems, but also for a variety of other precision experiments including the bounding of deviations from newtonian gravity at short distances and the measurement of single spins. Here, we demonstrate the use of a quantum point contact as a sensitive displacement detector capable of sensing the low-temperature thermal motion of a nearby micromechanical cantilever. Advantages of this approach include versatility due to its off-board design, compatibility with nanoscale oscillators and, with further development, the potential to achieve quantum-limited displacement detection. Nature Physics, vol. 4 #8, pp635-638 |