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Jian-Wei Pan

Publications and source records attributed to Jian-Wei Pan.

At least 469 records · Page 26Linked to original sources
arXiv2004

Experimental Free-Space Distribution of Entangled Photon Pairs over a Noisy Ground Atmosphere of 13km

We report free-space distribution of entangled photon pairs over a noisy ground atmosphere of 13km. It is shown that the desired entanglement can still survive after the two entangled photons have passed through the noisy ground atmosphere. This is confirmed by observing a space-like separated violation of Bell inequality of $2.45 \pm 0.09$. On this basis, we exploit the distributed entangled photon source to demonstrate the BB84 quantum cryptography scheme. The distribution distance of entangled photon pairs achieved in the experiment is for the first time well beyond the effective thickness of the aerosphere, hence presenting a significant step towards satellite-based global quantum communication.

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arXiv2004

Efficient Multi-Party Quantum Secret Sharing Schemes

In this work, we generalize the quantum secret sharing scheme of Hillary, Bužek and Berthiaume[Phys. Rev. A59, 1829(1999)] into arbitrary multi-parties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Bužek-Berthiaume quantum secret sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum secret sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis Quantum secret sharing scheme is developed from the Lo-Chau-Ardehali technique[H. K. Lo, H. F. Chau and M. Ardehali, quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted Quantum secret sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh and Y. D. Han, Phys. Lett. A244, 489 (1998)] where all participants choose their measuring-basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the GHZ-states in a quantum secret sharing process are used to generate shared secret information.

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arXiv2004

Realization of a photonic CNOT gate sufficient for quantum computation

We report the first experimental demonstration of a quantum controlled-NOT gate for different photons, which is classically feed-forwardable. In the experiment, we achieved this goal with the use only of linear optics, an entangled ancillary pair of photons and post-selection. The techniques developed in our experiment will be of significant importance for quantum information processing with linear optics.

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arXiv2004

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.

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arXiv2004

Experimental nonlinear sign shift for linear optics quantum computation

We have realized the nonlinear sign shift (NS) operation for photonic qubits.This operation shifts the phase of two photons reflected by a beam splitter using an extra single photon and measurement. We show that the conditional phase shift is $(1.05\pm 0.06) π$ in clear agreement with theory. Our results show that by using an ancilla photon and conditional detection, nonlinear optical effects can be implemented using only linear optical elements. This experiment represents an essential step for linear optical implementations of scalable quantum computation.

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arXiv2003

De Broglie Wavelength of a Nonlocal Four-Photon

Superposition is one of the most distinct features of quantum theory and has been demonstrated in numerous realizations of Young's classical double-slit interference experiment and its analogues. However, quantum entanglement - a significant coherent superposition in multiparticle systems - yields phenomena that are much richer and more interesting than anything that can be seen in a one-particle system. Among them, one important type of multi-particle experiments uses path-entangled number-states, which exhibit pure higher-order interference and allow novel applications in metrology and imaging such as quantum interferometry and spectroscopy with phase sensitivity at the Heisenberg limit or quantum lithography beyond the classical diffraction limit. Up to now, in optical implementations of such schemes lower-order interference effects would always decrease the overall performance at higher particle numbers. They have thus been limited to two photons. We overcome this limitation and demonstrate a linear-optics-based four-photon interferometer. Observation of a four-particle mode-entangled state is confirmed by interference fringes with a periodicity of one quarter of the single-photon wavelength. This scheme can readily be extended to arbitrary photon numbers and thus represents an important step towards realizable applications with entanglement-enhanced performance.

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arXiv2003

Deterministic and Highly Efficient Quantum Cryptography with Entangled Photon Pairs

We present a protocol for deterministic and highly efficient quantum cryptography with entangled photon pairs in a 4x4-dimentional Hilbert space. Two communicating parties, Alice and Bob first share a both polarization- and path-entangled photon pair, and then each performs a complete Bell-state measurement on their own photon in one of two complementary Bell-state bases. It is demonstrated that each measurement in which both Alice and Bob register a photon can build certain perfect correlation and generate 1.5 key bits on average. The security of our protocol is guaranteed by the non-cloning theorem.

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arXiv2003

An experimental observation of geometric phases for mixed states using NMR interferometry

Examples of geometric phases abound in many areas of physics. They offer both fundamental insights into many physical phenomena and lead to interesting practical implementations. One of them, as indicated recently, might be an inherently fault-tolerant quantum computation. This, however, requires to deal with geometric phases in the presence of noise and interactions between different physical subsystems. Despite the wealth of literature on the subject of geometric phases very little is known about this very important case. Here we report the first experimental study of geometric phases for mixed quantum states. We show how different they are from the well understood, noiseless, pure-state case.

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arXiv2003

All-Versus-Nothing Violation of Local Realism for Two Entangled Photons

It is shown that the Greenberger-Horne-Zeilinger theorem can be generalized to the case with only two entangled particles. The reasoning makes use of two photons which are maximally entangled both in polarization and in spatial degrees of freedom. In contrast to Cabello's argument of "all versus nothing" nonlocality with four photons [Phys. Rev. Lett. 87, 010403 (2001)], our proposal to test the theorem can be implemented with linear optics and thus is well within the reach of current experimental technology.

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arXiv2003

Experimental Test of Quantum Nonlocality in Four-photon Greenberger-Horne-Zeilinger Entanglement

We report the first experimental violation of local realism in four-photon Greenberger-Horne-Zeilinger (GHZ) entanglement. In the experiment, the non-statistical GHZ conflicts between quantum mechanics and local realism are confirmed, within the experimental accuracy, by four specific measurements of polarization correlations between four photons. In addition, our experimental results not only demonstrate a violation of Mermin-Ardehali-Belinskii-Klyshko inequality by 76 standard deviations, but also for the first time provide sufficient evidence to confirm the existence of genuine four-particle entanglement.

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arXiv2003

Concentration of higher dimensional entanglement

Enhancement of entanglement enhancement is necessary for most quantum communication protocols many of which are defined in Hilbert spaces larger than two. In this work we present the experimental realization of entanglement concentration of orbital angular momentum entangled photons produced in the spontaneous parametric down-conversion process which have been shown to provide a source for higher dimensional entanglement. We investigate the specific case of three dimensions and the possibility of generating different entangled states out of an initial state. The results presented here are of importance for pure states as well as for mixed states.

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arXiv2003

Experimental Realization of Entanglement Concentration and A Quantum Repeater

We report an experimental realization of entanglement concentration using two polarization-entangled photon pairs produced by pulsed parametric down-conversion. In the meantime, our setup also provides a proof-in-principle demonstration of a quantum repeater. The quality of our procedure is verified by observing a violation of Bell's inequality by more than 5 standard deviations. The high experimental accuracy achieved in the experiment implies that the requirement of tolerable error rate in multi-stage realization of quantum repeaters can be fulfilled, hence providing a practical toolbox for quantum communication over large distances.

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arXiv2003

Probabilistic instantaneous quantum computation

The principle of teleportation can be used to perform a quantum computation even before its quantum input is defined. The basic idea is to perform the quantum computation at some earlier time with qubits which are part of an entangled state. At a later time a generalized Bell state measurement is performed jointly on the then defined actual input qubits and the rest of the entangled state. This projects the output state onto the correct one with a certain exponentially small probability. The sufficient conditions are found under which the scheme is of benefit.

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arXiv2003

Perfect Test of Entanglement for Two-level Systems

A 3-setting Bell-type inequality enforced by the indeterminacy relation of complementary local observables is proposed as an experimental test of the 2-qubit entanglement. The proposed inequality has an advantage of being a sufficient and necessary criterion of the separability. Therefore any entangled 2-qubit state cannot escape the detection by this kind of tests. It turns out that the orientation of the local testing observables plays a crucial role in our perfect detection of the entanglement.

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arXiv2002

Implement Quantum Random Walks with Linear Optics Elements

The quantum random walk has drawn special interests because its remarkable features to the classical counterpart could lead to new quantum algorithms. In this paper, we propose a feasible scheme to implement quantum random walks on a line using only linear optics elements. With current single-photon interference technology, the steps that could be experimentally implemented can be extended to very large numbers. We also show that, by decohering the quantum states, our scheme for quantum random walk tends to be classical.

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arXiv2002

Correspondence between continuous variable and discrete quantum systems of arbitrary dimensions

We establish a mapping between a continuous variable (CV) quantum system and a discrete quantum system of arbitrary dimension. This opens up the general possibility to perform any quantum information task with a CV system as if it were a discrete system of arbitrary dimension. The Einstein-Podolsky-Rosen state is mapped onto the maximally entangled state in any finite dimensional Hilbert space and thus can be considered as a universal resource of entanglement. As an explicit example of the formalism a two-mode CV entangled state is mapped onto a two-qutrit entangled state.

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arXiv2002

Classifying N-qubit Entanglement via Bell's Inequalities

All the states of N qubits can be classified into N-1 entanglement classes from 2-entangled to N-entangled (fully entangled) states. Each class of entangled states is characterized by an entanglement index that depends on the partition of N. The larger the entanglement index of an state, the more entangled or the less separable is the state in the sense that a larger maximal violation of Bell's inequality is attainable for this class of state.

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