Research interest:   Quantum error correction   Quantum devices
Quantum memory
Quantum data must be stored within a physical system. One readily accessible physical system is the Heisenberg ferromagnet, which has as its ground space the set of all symmetric states. By storing quantum data within a symmetric code, one can benefit from (1) the fact that such codes are left unchanged by the underlying dynamics of the Heisenberg ferromagnet, and (2) the quantum error correction properties of these symmetric codes.Â
I calculate bounds on the error of such quantum storage under physically realistic conditions. This calculation does not rely on any specific properties of symmetric codes apart from the number of errors they can correct. Hence, all symmetric codes with QEC properties can be used. Also I use the fact that the spectral gap of the Heisenberg ferromagnet can grow with the system size.
Related papers:
2019   Quantum storage in quantum ferromagnets        Â
Y. Ouyang   Physical Review B 103, 14417
2019  Computing spectral bounds of the Heisenberg ferromagnet from geometric considerations Â
Y. Ouyang   Journal of Mathematical Physics 60 (7) 017901
Quantum Metrology
In the quantum metrology problem, one wishes to use a quantum resource to measure a signal with known structure but unknown strength. Quantum metrology does not require the full power of quantum computation, and might serve as an early use-case for quantum technologies.
The quantum resource in quantum metrology are probe states. Probe states are unfortunately fragile, and need to be designed to be robust against errors. Surprisingly, entanglement in a probe state, while necessary for quantum metrology, is not sufficient to allow robust metrology. The search for robust probe states is non-trivial, and symmetric probe states are good candidates.
Eventually quantum metrology will integrate with quantum error correction, to allow measurements to attain their maximum precision, namely via fault tolerant quantum metrology.
Related papers:
2020 Â Â Weight distribution of classical codes influences quantum metrology
Yingkai Ouyang, N. Rengaswamy http://arxiv.org/abs/2007.02859
2019  Tight bounds on the simultaneous estimation of incompatible parameters  Â
J. S. Sidhu, Yingkai Ouyang, E. T. Campbell, P. Kok   Physical Review X 11, 011028
2019 Â Â Robust quantum metrology with explicit symmetric states
Yingkai Ouyang, N. Shettell, D. Markham   http://arxiv.org/abs/1908.02378
Quantum computer
With respect to quantum computations, I am interested in (1) permutational quantum computation, (2) quantum simulation and (3) the resource theory of quantum computation.
Related Papers:
2020 Â Â Quantifying quantum speedups:Â improved classical simulation from tighter magic monotones
J.R. Seddon, B. Regula, H. Pashayan, Y. Ouyang, E.T. Campbell  PRX Quantum 2 (1), 010345Â
2020Â Â Compilation by Hamiltonian Sparsification
Yingkai Ouyang, D.R. White, E.T. Campbell  Quantum ,4 235
2019   Faster quantum computation with permutations and resonant couplings Â
Yingkai Ouyang, Y. Shen, L. Chen   Linear Algebra and its Applications 592, 270-286
2018   Classical verification of quantum circuits containing few basis changes Â
T.F. Demarie, Yingkai Ouyang, J.F. Fitzsimons   Physical Review A 97, 042319 Â
Quantum security
I have also worked in quantum cryptography, using my expertise of quantum information and quantum coding theory.
Related papers:
2020   Homomorphic encryption of linear optics quantum computation on almost arbitrary states of light with asymptotically perfect security Â
Yingkai Ouyang, S.H. Tan, J.F.Fitzsimons, P.P. Rohde   Physical Review Research 2, 013332
2018 Quantum homomorphic encryption from quantum codesÂ
Yingkai Ouyang, S.H. Tan, J. Fitzsimons    Physical Review A 98, 042334
2018 Practical quantum somewhat-homomorphic encryption with coherent states
S.H. Tan, Yingkai Ouyang, P. Rohde    Physical Review A 97, 042308
2017   Computing on quantum shared secrets Â
Yingkai Ouyang, S.H. Tan, L. Zhao, J. Fitzsimons   Physical Review A 96, 052333
2016  A quantum approach to homomorphic encryption Â
S.H. Tan, J. Kettlewell, Yingkai Ouyang, L. Chen, J. Fitzsimons   Scientific Reports 6, 042340Â