Experimental Demonstration of Five-photon Entanglement and Open-destination Teleportation

Universal quantum error-correction requires the ability of manipulating entanglement of five or more particles. Although entanglement of three or four particles has been experimentally demonstrated and used to obtain the extreme contradiction between quantum mechanics and local realism, the realization of five-particle entanglement remains an experimental challenge. Meanwhile, a crucial experimental challenge in multi-party quantum communication and computation is the so-called open-destination teleportation. During open-destination teleportation, an unknown quantum state of a single particle is first teleported onto a N-particle coherent superposition to perform distributed quantum information processing. At a later stage this teleported state can be readout at any of the N particles for further applications by performing a projection measurement on the remaining N-1 particles. Here, we report a proof-of-principle demonstration of five-photon entanglement and open-destination teleportation. In the experiment, we use two entangled photon pairs to generate a four-photon entangled state, which is then combined with a single photon state to achieve the experimental goals. The methods developed in our experiment would have various applications e.g. in quantum secret sharing and measurement-based quantum computation.Comment: 19 pages, 4 figures, submitted for publication on 15 October, 200

Quantum time of flight distribution for cold trapped atoms

The time of flight distribution for a cloud of cold atoms falling freely under gravity is considered. We generalise the probability current density approach to calculate the quantum arrival time distribution for the mixed state describing the Maxwell-Boltzmann distribution of velocities for the falling atoms. We find an empirically testable difference between the time of flight distribution calculated using the quantum probability current and that obtained from a purely classical treatment which is usually employed in analysing time of flight measurements. The classical time of flight distribution matches with the quantum distribution in the large mass and high temperature limits.Comment: 6 pages, RevTex, 4 eps figure

Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50-300 k$\Omega$. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltages. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory.Comment: 4 pages, REVTeX, submitted to PR

A Factorization Law for Entanglement Decay

We present a simple and general factorization law for quantum systems shared by two parties, which describes the time evolution of entanglement upon passage of either component through an arbitrary noisy channel. The robustness of entanglement-based quantum information processing protocols is thus easily and fully characterized by a single quantity.Comment: 4 pages, 5 figure

Highly sensitive, stretchable and durable strain sensors based on conductive double-network polymer hydrogels

Hydrogel-based strain sensors have been attracting immense attention for wearable electronic devices owing to their intrinsic soft characteristics and flexibility. However, developing hydrogel sensors with hightensile strength, stretchability, and strain sensitivity remains a great challenge. Herein, we report a technique to synthesize highly sensitive hydrogel-based strain sensors by integrating carbon nanofibers (CNFs) with a double-network (DN) polymer hydrogel matrix comprising of a physically cross-linked agar network and a covalently cross-linked polyacrylamide (PAAm) network. The resultant nanocomposite sensors display superior piezoresistive sensitivity with a hightrue gauge factor (GFT = 1.78) at an ultrahigh strain of 1,000%, a fast response time and linear correlation of ln(R/R0) and ln(L/L0) up to 1,000% strain. Most significantly, these sensors possess highmechanical strength (~0.6 MPa) and superb durability (>1,000 cycles at strain of 100%), stemming from the effective energy dissipation mechanism of the first agar network acting as sacrificial bonds and the CNFs serving as dynamic nanofillers. The combination of highstrain sensitivity and ultrahigh stretchability of hydrogel sensors makes it possible to sense both small mechanical deformations induced by human motions and large strain up to 1,000%

Experimental Quantum Teleportation of a Two-Qubit Composite System

Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with photonic or ionic qubits. Very recently long-distance teleportation and open-destination teleportation have also been realized. Until now, previous experiments have only been able to teleport single qubits. However, since teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation2-5, teleportation of a composite system containing two or more qubits has been seen as a long-standing goal in quantum information science. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols such as multi-stage realization of quantum-relay, fault-tolerant quantum computation, universal quantum error-correction and one-way quantum computation.Comment: 16pages, 4 figure

Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates

Physical effects of bilayer coupling on the tunneling spectroscopy of high T$_{c}$ cuprates are investigated. The bilayer coupling separates the bonding and antibonding bands and leads to a splitting of the coherence peaks in the tunneling differential conductance. However, the coherence peak of the bonding band is strongly suppressed and broadened by the particle-hole asymmetry in the density of states and finite quasiparticle life-time, and is difficult to resolve by experiments. This gives a qualitative account why the bilayer splitting of the coherence peaks was not clearly observed in tunneling measurements of double-layer high-T$_c$ oxides.Comment: 4 pages, 3 figures, to be published in PR

Inherent Inhomogeneities in Tunneling Spectra of BSCCO Crystals in the Superconducting State

Scanning Tunneling Spectroscopy on cleaved BSCCO(2212) single crystals reveal inhomogeneities on length-scales of $\sim$30 $\AA$. While most of the surface yields spectra consistent with a d-wave superconductor, small regions show a doubly gapped structure with both gaps lacking coherence peaks and the larger gap having a size typical of the respective pseudo-gap for the same sample.Comment: 4 pages, 4 figure

Anti-phase Modulation of Electron- and Hole-like States in Vortex Core of Bi2Sr2CaCu2Ox Probed by Scanning Tunneling Spectroscopy

In the vortex core of slightly overdoped Bi2Sr2CaCu2Ox, the electron-like and hole-like states have been found to exhibit spatial modulations in anti-phase with each other along the Cu-O bonding direction. Some kind of one-dimensionality has been observed in the vortex core, and it is more clearly seen in differential conductance maps at lower biases below +-9 mV

Staggered local density-of-states around the vortex in underdoped cuprates

We have studied a single vortex with the staggered flux (SF) core based on the SU(2) slave-boson theory of high $T_c$ superconductors. We find that whereas the center in the vortex core is a SF state, as one moves away from the core center, a correlated staggered modulation of the hopping amplitude $\chi$ and pairing amplitude $\Delta$ becomes predominant. We predict that in this region, the local density-of-states (LDOS) exhibits staggered modulation when measured on the bonds, which may be directly detected by STM experiments.Comment: 4 pages, 3 figure