-Ping Guo

Quantum secret sharing without entanglement

After analysing the main quantum secret sharing protocol based on the entanglement states, we propose an idea to directly encode the qubit of quantum key distributions, and then present a quantum secret sharing scheme where only product states are employed. As entanglement, especially the inaccessible multi-entangled state, is not necessary in the present quantum secret sharing protocol, it may be more applicable when the number of the parties of secret sharing is large. Its theoretic efficiency is also doubled to approach 100%.

Scheme for the preparation of multiparticle entanglement in cavity QED

Here we present a quantum electrodynamics model involving a large-detuned single-mode cavity field and n identical two-level atoms. One of its applications for the generation of multiparticle entangled states of various kinds (Greenberger-Horne-Zeilinger states and different class of so-called W states) is analyzed. The theoretical prediction for the model of

A graphene quantum dot with a single electron transistor as an integrated charge sensor

n=2

Ultrafast universal quantum control of a quantum-dot charge qubit using Landau–Zener–Stückelberg interference

is made that is consistent with the experimental result by considering the possible three-atom collisions.

Strong and Tunable Spin−Orbit Coupling of One-Dimensional Holes in Ge/Si Core/Shell Nanowires

A quantum dot (QD) with an integrated charge sensor is becoming a common architecture for a spin or charge based solid state qubit. To implement such a structure in graphene, we have fabricated a twin-dot structure in which the larger dot serves as a single electron transistor (SET) to read out the charge state of the nearby gate controlled small QD. A high SET sensitivity of 10−3e/Hz allowed us to probe Coulomb charging as well as excited state spectra of the QD, even in the regime where the current through the QD is too small to be measured by conventional transport means.

Coupling of light from an optical fiber taper into silver nanowires

A basic requirement for quantum information processing is the ability to universally control the state of a single qubit on timescales much shorter than the coherence time. Although ultrafast optical control of a single spin has been achieved in quantum dots, scaling up such methods remains a challenge. Here we demonstrate complete control of the quantum-dot charge qubit on the picosecond scale, orders of magnitude faster than the previously measured electrically controlled charge- or spin-based qubits. We observe tunable qubit dynamics in a charge-stability diagram, in a time domain, and in a pulse amplitude space of the driven pulse. The observations are well described by Landau–Zener–Stückelberg interference. These results establish the feasibility of a full set of all-electrical single-qubit operations. Although our experiment is carried out in a solid-state architecture, the technique is independent of the physical encoding of the quantum information and has the potential for wider applications.

Generation of quantum-dot cluster States with a superconducting transmission line resonator.

We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin--orbit coupling. The temperature and back gate dependences of phase coherence length, spin--orbit relaxation time, and background conductance were studied. Specifically, we show that the spin--orbit coupling strength can be modulated by more than five folds with an external electric field. These results suggest the Ge/Si nanowire system possesses strong and tunable spin--orbit interactions and may serve as a candidate for spintronics applications.

Plasmon-assisted transmission of high-dimensional orbital angular-momentum entangled state

We report the coupling of photons from an optical fiber taper to surface plasmon modes of silver nanowires. The coupling efficiency can be modulated by adjusting the cross angle and the polarization of the input light. The launch of propagating plasmons can be realized not only at ends of the nanowires but also at the midsection. In addition, we present the coupling of light into multiple nanowires from a single optical fiber taper simultaneously. Our demonstration offers an efficient method for optimizing plasmon coupling into nanoscale metallic waveguides and promotes the realization of highly integrated plasmonic devices.

Detecting orbital angular momentum through division-of-amplitude interference with a circular plasmonic lens.

We propose an efficient method to generate cluster states in spatially separated double quantum dots with a superconducting transmission line resonator. When the detuning between the double-dot qubit transition frequency and the frequency of the full wave mode in the transmission line resonator satisfies some conditions, an Ising-like operator between an arbitrary two separated qubits can be achieved. Even including the main noise sources, it is shown that the high fidelity cluster states could be generated in this solid system in just one step.

Quantum computation with graphene nanoribbon

We present an experimental evidence that high-dimensional orbital angular-momentum entanglement of a pair of photons can be survived after a photon-plasmon-photon conversion. The information of spatial modes can be coherently transmitted by surface plasmons. This experiment primarily studies the high-dimensional entangled systems based on surface plasmon with subwavelength structures. It maybe useful in the investigation of spatial-mode properties of surface plasmon-assisted transmission through subwavelength hole arrays.