Inelastic neutron scattering was employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe$_{0.953}$Co$_{0.047}$)$_{2}$As$_{2}$. These materials are ideal to study the paramagnetic-nematic state, sinc
e the nematic order, signaled by the tetragonal-to-orthorhombic transition at $T_{{rm S}}$, sets in well above the stripe antiferromagnetic ordering at $T_{{rm N}}$. We find that the temperature-dependent dynamic susceptibility displays an anomaly at $T_{{rm S}}$ followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that attributes the structural/nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.
Quantum computers promise dramatic speed ups for many computational tasks. For large-scale quantum computation however, the inevitable coupling of physical qubits to the noisy environment imposes a major challenge for a real-life implementation. A sc
heme introduced by Gottesmann and Chuang can help to overcome this difficulty by performing universal quantum gates in a fault-tolerant manner. Here, we report a non-trivial demonstration of this architecture by performing a teleportation-based two-qubit controlled-NOT gate through linear optics with a high-fidelity six-photon interferometer. The obtained results clearly prove the involved working principles and the entangling capability of the gate. Our experiment represents an important step towards the feasibility of realistic quantum computers and could trigger many further applications in linear optics quantum information processing.
This paper studies colimits of sequences of finite Chu spaces and their ramifications. Besides generic Chu spaces, we consider extensional and biextensional variants. In the corresponding categories we first characterize the monics and then the exist
ence (or the lack thereof) of the desired colimits. In each case, we provide a characterization of the finite objects in terms of monomorphisms/injections. Bifinite Chu spaces are then expressed with respect to the monics of generic Chu spaces, and universal, homogeneous Chu spaces are shown to exist in this category. Unanticipated results driving this development include the fact that while for generic Chu spaces monics consist of an injective first and a surjective second component, in the extensional and biextensional cases the surjectivity requirement can be dropped. Furthermore, the desired colimits are only guaranteed to exist in the extensional case. Finally, not all finite Chu spaces (considered set-theoretically) are finite objects in their categories. This study opens up opportunities for further investigations into recursively defined Chu spaces, as well as constructive models of linear logic.
A periodically poled lithium niobate (PPLN) waveguide-based single-pixel up-conversion infrared spectrometer was demonstrated. Sum-frequency generation between a 1.5 micrometer band scanning pump laser and a 1.3 micrometer band signal generated visib
le radiation which was detected by a silicon single-photon detector. The noise equivalent power of the upconversion spectrometer was two-orders-of-magnitude lower than that of a commercial optical spectrum analyzer.
We report an experimental demonstration of entanglement swapping over two quantum stages. By successful realizations of two cascaded photonic entanglement swapping processes, entanglement is generated and distributed between two photons, that origina
te from independent sources and do not share any common past. In the experiment we use three pairs of polarization entangled photons and conduct two Bell-state measurements (BSMs) one between the first and second pair, and one between the second and third pair. This results in projecting the remaining two outgoing photons from pair 1 and 3 into an entangled state, as characterized by an entanglement witness. The experiment represents an important step towards a full quantum repeater where multiple entanglement swapping is a key ingredient.
In this letter, we report an experimental realization of distributing entangled photon pairs over 100 km of dispersion-shifted fiber. In the experiment, we used a periodically poled lithium niobate waveguide to generate the time-energy entanglement a
nd superconducting single-photon detectors to detect the photon pairs after 100 km. We also demonstrate that the distributed photon pairs can still be useful for quantum key distribution and other quantum communication tasks.
We report an experimental realization of one-way quantum computing on a two-photon four-qubit cluster state. This is accomplished by developing a two-photon cluster state source entangled both in polarization and spatial modes. With this special sour
ce, we implemented a highly efficient Grovers search algorithm and high-fidelity two qubits quantum gates. Our experiment demonstrates that such cluster states could serve as an ideal source and a building block for rapid and precise optical quantum computation.
Feedstock and byproduct diffusion in the root growth of aligned CNT arrays was discussed in this work. A non-dimensional modulus was proposed to differentiate catalyst-decay controlled growth deceleration from diffusion controlled one. It was found t
hat aligned MWNT arrays are usually free of feedstock diffusion while SWNT arrays are usually facing strong diffusion limit. The present method can also be utilized to predict the maximum length that CNT forest can grow in certain CVD process.
