CAS Researchers Make Breakthrough in Hyper-Entangled Schr dinger Cat State

Quantum entanglement is the crucial resource for quantum information processing, which is a very competitive research topic in the quantum information field. In 2000, the National Institute of Standards and Technology (NIST, USA) demonstrated the four-ion entanglement. In 2004, the researchers from the same QPQI Division broke the record, and successfully created a five-photon entangled state. In the end of 2005, two groups from NIST and the Innsbruck University, Austria announced the demonstration of six and eight-ion entangled states respectively, and had kept the record since then.

a,b, Coincidence counts obtained in the |H/|V (|H /|V ) basis, accumulated for 150 s and 480 s for the six- (a) and eight-qubit (b) state respectively. c,d, Measurement results obtained along the basis of , showing the coherence of the cat states and phase super-resolution fringes (see text). The error bars represent one standard deviation (in c they are smaller than the dots representing the measurement points) deduced from propagated Poissonian counting statistics of the raw detection events. (Picture/QPQI)

How to efficiently expand the number of entangled qubits is a great challenge in quantum information field. PAN Jianwei, CHEN Zengbing, PENG Chengzhi and coworkers aware that each degree of the freedom of a single photon can be defined as a quantum bit under suitable conditions. These different degrees of freedom can be used to form an entangled state, the so-called hyper-entangled state. This idea provides an effective method to expand the number of entangled quantum bits. Using this idea the research group realized the 10-qubit Schr dinger cat state based on a five-photon polarization entangled state and thereby demonstrated entanglement-based phase super-resolution.

This work has attracted widespread attention in the international academic community. As soon as the e-print of the reported work appears on the arXiv, physicsworld.com reported the news under the title Physicists set new entanglement record and regarded the work as an important breakthrough in practical quantum computer .

According to the researchers introduction, the concept of Schr dinger cat states comes from a well-known paradox: there is a cat inside the box which can be simultaneously dead and alive. Although a macroscopic Schr dinger cat state does not exist in the macroworld, it does exist in the microscopic quantum world. Scientists can use photons or atoms to create such a state.

Paper abstract: http://www.nature.com/nphys/journal/v6/n5/abs/nphys1603.html