Xiao-Hui Bao

Observation of eight-photon entanglement

Researchers demonstrate the creation of an eight-photon Schrodinger-cat state with genuine multipartite entanglement by developing noise-reduction multiphoton interferometer and post-selection detection. The ability to control eight individual photons will enable new multiphoton entanglement experiments in previously inaccessible parameter regimes.

Experimental Free-Space Distribution of Entangled Photon Pairs Over 13 km: Towards Satellite-Based Global Quantum Communication

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

Experimental demonstration of a heralded entanglement source

2.45 \pm 0.09

Generation of Narrow-Band Polarization-Entangled Photon Pairs for Atomic Quantum Memories

. 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.

A millisecond quantum memory for scalable quantum networks

An efficient source of entangled photons generated in an event-ready manner by conditioned detection of auxiliary photons is reported. A fidelity better than 87% and a state preparation efficiency of 45% are obtained. The scheme could offer promising applications in essential photonics-based quantum information tasks, and represents a particularly important development in the realization of optical quantum computing.

Efficient and long-lived quantum memory with cold atoms inside a ring cavity

We report an experimental realization of a narrow band polarization-entangled photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous parametric down-conversion. This linewidth is comparable to the typical linewidth of atomic ensemble-based quantum memories. Single-mode output is realized by setting a reasonable cavity length difference between different polarizations, using of temperature controlled etalons and actively stabilizing the cavity. The entangled property is characterized with quantum state tomography, giving a fidelity of 94% between our state and a maximally entangled state. The coherence length is directly measured to be 32 m through two-photon interference.

Optical nondestructive controlled-NOT gate without using entangled photons

calculation shows that the expected lifetime is of the order of seconds in this case. Here we report on our investigation of prolonging the storage time of the quantum memory for single excitations. In the experiment, we find that using only the ‘clock state’ is not sufficient toobtain theexpected longstorage time.We furtheranalyse, isolate and identify the distinct decoherence mechanisms, and thoroughly investigate the dephasing of the spin wave (SW) by varying its wavelength. We find that the dephasing of the SW is extremely sensitive to the angle between the write beam and detection mode, especiallyforsmallangles.Onthebasisofthisfinding,byexploiting the ‘clock state’ and increasing the wavelength of the SW to suppress the dephasing, we succeed in extending the storage time from 10s

An efficient quantum light–matter interface with sub-second lifetime

A quantum memory that combines high-efficiency and long lifetime is now demonstrated. Employing a collective excitation, or spin wave, in an ensemble of atoms in a trap improves memory lifetime, while incorporating the trap into an optical ring cavity simultaneously aids higher retrieval efficiency. Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation1 and long-distance quantum communication2. A long-standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived3,4 or long-lived but inefficient quantum memories5,6,7 have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a long-wavelength spin wave and arranging the set-up in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1) ms. This realization provides an essential tool towards scalable linear-optical quantum information processing.

Quantum teleportation between remote atomic-ensemble quantum memories

We present and experimentally demonstrate a novel optical nondestructive controlled-NOT gate without using entangled ancilla. With much fewer measurements compared with quantum process tomography, we get a good estimation of the gate fidelity. The result shows a great improvement compared with previous experiments. Moreover, we also show that quantum parallelism is achieved in our gate and the performance of the gate can not be reproduced by local operations and classical communications.

Heralded generation of an atomic NOON state.

An efficient light–matter interface for quantum repeaters is developed. By placing Rb atoms optically confined in a 3D lattice in a ring cavity, an initial retrieval efficiency of 76% together with a 1/e lifetime of 0.22 s are achieved.