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Guang-Can Guo

Publications and source records attributed to Guang-Can Guo.

At least 883 records · Page 49Linked to original sources
arXiv2008

Entanglement of the orbital angular momentum states of the photons generated in a hot atomic ensemble

Quantum protocols will be more efficient with high-dimensional entangled states. Photons carrying orbital angular momenta can be used to create a high-dimensional entangled state. In this paper we experimentally demonstrate the entanglement of the orbital angular momentum between the Stokes and anti-Stokes photons generated in a hot atomic ensemble using spontaneous four-wave-mixing. This experiment also suggests the existence of the entanglement concerned with spatial degrees of freedom between the hot atomic ensemble and the Stokes photon.

quant-ph↗
arXiv2008

Quantum interference of multimode two-photon pairs with a Michelson interferometer

We experimentally observe the two-photon interference of multimode photon pairs produced by an optical parametric oscillator far below threshold via a michelson interferometer, which shows a multipeaked structure. We find that the correlation function when the interferometer is unbalanced is clearly dependent on the path difference and phase between two interfering beams, but the shape of correlation function in balanced case is independent on the small path difference and phase beside the height. All experimental results are well agreed with the theoretical prediction.

quant-ph↗
arXiv2008

Observation of time correlation function of multimode two-photon pairs on a rubidium D$_2$ line

We report the generation of a type-I multimode two-photon state on a rubidium D$_2$ line (780 nm) using periodically poled KTiOPO$_4$ crystals. With a degenerate optical parametric oscillator far below threshold, we observe an oscillatory correlation function, the cross-correlation between two photons shows a cavity bandwidth of about 7.8 MHz. We also use a Fabry-P$\acute{\rm{e}}$rot etalon to filter its most longitudinal modes and observe its time correlation function. The experimental data are well fitted to theoretical curves. This system could be utilized for demonstrating storage and retrieval of narrowband photons in Rb atomic ensembles, which is important for long-distance quantum communication.

quant-ph↗
arXiv2008

Removal of surface plasmon polariton eigenmodes degeneracy

The effect of the tilt angle of metal film on the transmissivity of subwavelength holes in optically thick metal film is investigated. The transmission efficiency is found can be highly dependent on the tilt angle. It is also found that when the input photons are polarized not along the eigenmode directions of surface plasmon polariton, a birefringent phenomenon is observed when the array with periodic of subwavelength holes is tilted. Linear polarization states can be changed to elliptical polarization states and a phase can be added between two eigenmodes. The phase is changed with the tilt angle. A model based on surface plasmon polariton eigenmodes degeneracy is presented to explain these experimental results.

physics.optics↗
arXiv2008

Polarization properties of subwavelength hole arrays consisting of rectangular holes

Influence of hole shape on extraordinary optical transmission was investigated using hole arrays consisting of rectangular holes with different aspect ratio. It was found that the transmission could be tuned continuously by rotating the hole array. Further more, a phase was generated in this process, and linear polarization states could be changed to elliptical polarization states. This phase was correlated with the aspect ratio of the holes. An intuitional model was presented to explain these results.

physics.optics↗
arXiv2008

Interference of surface plasmon polaritions controlled by the phase of incident light

Interference patterns of surface plasmon polaritons(SPPs) are observed in the extraordinary optical transmission through subwavelength holes in optically thick metal plate. It is found that the phase of incident light can be transferred to SPPs. We can control the destructive and constructive interference of SPPs by modulating the relative phase between two incident beams. Using a slightly displaced Mach-Zehnder interferometer, we also observe a SPPs interference pattern composed of bright and dark stripes.

physics.optics↗
arXiv2008

Entanglement detection beyond the cross-norm or realignment criterion

Separability problem, to decide whether a given state is entangled or not, is a fundamental problem in quantum information theory. We propose a powerful and computationally simple separability criterion, which allows us to detect the entanglement of many bound entangled states. The criterion is strictly stronger than the dV criterion, the computable cross-norm or realignment criterion and its optimal nonlinear entanglement witnesses. Furthermore, this criterion can be generalized to an analogue of permutation separability criteria in the even-partite systems.

quant-ph↗
arXiv2008

Highly-reduced Fine-structure splitting in InAs/InP quantum dots offering efficient on-demand 1.55 $μ$m entangled photon emitter

To generate entangled photon pairs via quantum dots (QDs), the exciton fine structure splitting (FSS) must be comparable to the exciton homogeneous line width. Yet in the (In,Ga)As/GaAs QD, the intrinsic FSS is about a few tens $μ$eV. To achieve photon entanglement, it is necessary to Cherry-pick a sample with extremely small FSS from a large number of samples, or to apply strong in-plane magnetic field. Using theoretical modeling of the fundamental causes of FSS in QDs, we predict that the intrinsic FSS of InAs/InP QDs is an order of magnitude smaller than that of InAs/GaAs dots, and better yet, their excitonic gap matches the 1.55 $μ$m fiber optic wavelength, therefore offer efficient on-demand entangled photon emitters for long distance quantum communication.

cond-mat.mtrl-sci↗
arXiv2008

Computational Complexity of Continuous Variable Quantum Key Distribution

The continuous variable quantum key distribution has been considered to have the potential to provide high secret key rate. However, in present experimental demonstrations, the secret key can be distilled only under very small loss rates. Here, by calculating explicitly the computational complexity with the channel transmission, we show that under high loss rate it is hard to distill the secret key in present continuous variable scheme and one of its advantages, the potential of providing high secret key rate, may therefore be limited.

quant-ph↗
arXiv2008

Dispersive Coupling Between the Superconducting Transmission Line Resonator and the Double Quantum Dots

Realization of controllable interaction between distant qubits is one of the major problems in scalable solid state quantum computing. We study a superconducting transmission line resonator (TLR) as a tunable dispersive coupler for the double-dot molecules. A general interaction Hamiltonian of $n$ two-electron spin-based qubits and the TLR is presented, where the double-dot qubits are biased at the large detuning region and the TLR is always empty and virtually excited. Our analysis o the main decoherence sources indicates that various major quantum operations can be reliably implemented with current technology.

quant-ph↗
arXiv2008

Giant optical anisotropy in cylindrical self-assembled InAs/GaAs quantum rings

Using a single-particle atomistic pseudopotential method followed by a many-particle configuration interaction method, we investigate the geometry, electronic structure and optical transitions of a self-assembled InAs/GaAs quantum ring (QR), changing its shape continously from a lens-shaped quantum dot (QD) to a nearly one dimensional ring. We find that the biaxial strain in the ring is strongly asymmetric in the plane perpendicular to the QR growth direction, leading to giant optical anisotropy.

cond-mat.mtrl-sci↗
arXiv2008

Eliminating interactions between non-neighboring qubits in the preparation of cluster states in quantum molecules

We propose a scheme to eliminate the effect of non-nearest-neighbor qubits in preparing cluster state with double-dot molecules. As the interaction Hamiltonians between qubits are Ising-model and mutually commute, we can get positive and negative effective interactions between qubits to cancel the effect of non-nearest-neighbor qubits by properly changing the electron charge states of each quantum dot molecule. The total time for the present multi-step cluster state preparation scheme is only doubled for one-dimensional qubit chain and tripled for two-dimensional qubit array comparing with the time of previous protocol leaving out the non-nearest-neighbor interactions.

quant-ph↗
arXiv2008

Permutation-invariant monotones for multipartite entanglement characterization

In this work we consider the permutational properties of multipartite entanglement monotones. Based on the fact that genuine multipartite entanglement is a property of the entire multi-qubit system, we argue that ideal definitions for its characterizing quantities must be permutation-invariant. Using this criterion, we examine the three 4-qubit entanglement monotones introduced by Osterloh and Siewert [Phys. Rev. A. 72, 012337]. By expressing them in terms of quantities whose permutational properties can be easily derived, we find that one of these monotones is not permutation-invariant. We propose a permutation-invariant entanglement monotone to replace it, and show that our new monotone properly measures the genuine 4-qubit entanglement in 4-qubit cluster-class states. Our results provide some useful insights in understanding multipartite entanglement.

quant-ph↗
arXiv2008

Methods for linear optical quantum Fredkin gate

We consider the realization of quantum Fredkin gate with only linear optics and single photons. First we construct a heralded Fredkin gate using four heralded controlled-not (CNOT) gates. Then we simplify this method to a post-selected one utilizing only two CNOT gates. We also give a possible realization of this method which is feasible with current experimental technology. Another post-selected scheme requires time entanglement of the input photons but needs no ancillary photons.

quant-ph↗
arXiv2008

Robust quantum cryptography with a heralded single-photon source based on the decoy-state method

In this paper, we describe a robust quantum cryptography scheme with a heralded single photon source based on the decoy-state method, which has been shown by numerical simulations to be advantageous compared with many other practical schemes not only with respect to the secure key generation rate but also to secure transmission distance. We have experimentally tested this scheme, and the results support the conclusions from numerical simulations well. Although there still exist many deficiencies in our present systems, it's still sufficient to demonstrate the advantages of the scheme. Besides, even when cost and technological feasibility are taken into account, our scheme is still quite promising in the implementation of tomorrow's quantum cryptography.

quant-ph↗
arXiv2008

Decoy states for quantum key distribution based on decoherence-free subspaces

Quantum key distribution with decoherence-free subspaces has been proposed to overcome the collective noise to the polarization modes of photons flying in quantum channel. Prototype of this scheme have also been achieved with parametric-down conversion source. However, a novel type of photon-number-splitting attack we proposed in this paper will make the practical implementations of this scheme insecure since the parametric-down conversion source may emit multi-photon pairs occasionally. We propose decoy states method to make these implementations immune to this attack. And with this decoy states method, both the security distance and key bit rate will be increased.

quant-ph↗
arXiv2008

Automated and robust population transfer method for three-level system using oscillating dark states

An automated and robust method for adiabatic population transfer and the preparation of an arbitrary quantum superposition state in atomic system using the oscillating dark states (ODS) is presented. Quantum state of a three-level $Λ$ configuration atomic system oscillates periodically between two ground levels, when two pairs of classical detuning laser fields driving the system into the ODS under evolving adiabatic conditions. The decoherence of the ODS evolution is greatly suppressed, and the oscillation is very stable, therefore adiabatic population transfer and the preparation of an arbitrary quantum superposition state of atomic system can be completed accurately and conveniently.

quant-ph↗