Experimental Demonstration Of Topological Error Correction And Production Of A Bose-Fermi Superfluid Mixture Of ⁴¹K And ⁶Li

This thesis mainly consists of two different parts. The first part is about the exper-imental demonstration of topological error correction with multi-photon entanglement. Hntanglement is the core resource of quantum computation. Linear optical quantum system enjoys the limelight for the reason that the coupling of photons with the envi-ronment is relatively weak comparing with other systems leading to a longer decoher-ence time. Moreover, linear optical elements of optical systems may be the simplest building blocks to realize quantum operations and quantum gates. However, the ubiq-uitous decoherence of quantum states makes it hard to achieve the required degree of quantum control. Quantum error correction has been invented in order to overcome this problem. Topological error correction uses the topological feature of the cluster state and only requires nearest-neighbour interactions. The threshold error rate is as high as 1%. which is three orders of magnitude higher than previous schemes. Cluster state is a highly-entangled quantum state which is the universal resource for one-way quantum computation. Based on an ultrabright, high-fidelity entangled photon source, we cre-ate the desired eight-photon cluster state and successfully experimental demonstrate the topological error correction. The witness of the state is about-0.105 ± 0.023, which is negative by 4.5 standard deviation. We proof that topological error correction can be protected against a single error on any quantum bit. Furthermore, the effective error rate can be greatly reduced, when all quantum bits are simultaneously suffered from errors with equal probability. Our work sheds a new light on error-tolerant quantum computation.The second part of my thesis is about a new apparatus of ultracold Bose-Fermi quantum degenerate mixture. We are able to cool both4'K and 6Li atoms to the quantum degeneracy. The experimental procedure consists of Zeeman slower,2D'MOT,3D MOT, UV MOT. gray molasses, optical pumping, magnetic transport, evaporation in the plugged magnetic trap and optical dipole trap. In the plugged magnetic trap, we can achieve a degenerate Bose-Fermi mixture with 1.4 × 105 41K atoms and 5.5 × 105 6Li atoms. The temperature of 41K is about 72.4% Tc, while the temperature of 6Li is about 25% TF. In the optical dipole trap, we attain an even better result. The atom number of 41K condensate is about 1.8 x 105 without discernable thermal fraction and the atom number of spin mixture 6Li atoms is about 1.5 x 106 with 7% Fermi temperature. It is for the first time in the world that a heteronuclear Bose-Fermi double superfluid mixture is generated. Based on these achievements, we rotate the superfluid mixture and observe the quantized coupled vortex lattices. We also go into more details on the nucleation and evolution of the coupled vortex lattices and find out many nontrivial effects. These results will no doubt promote the deeper understanding of superfluidity and high-Tc superconductivity.