Huan-Yu Ku

Accelerating multipartite entanglement generation in non-Hermitian superconducting qubits

  1. Chimdessa Gashu Feyisa,
  2. J. S. You,
  3. Huan-Yu Ku,
  4. and H. H. Jen
Open quantum systems are susceptible to losses in information, energy, and particles due to their surrounding environment. One novel strategy to mitigate these losses is to transform
them into advantages for quantum technologies through tailored non-Hermitian quantum systems. In this work, we theoretically propose a fast generation of multipartite entanglement in non-Hermitian qubits. Our findings reveal that weakly coupled non-Hermitian qubits can accelerate multiparty entanglement generation by thousands of times compared to Hermitian qubits, in particular when approaching the 2n-th order exceptional points of n qubits in the − symmetric regime. Furthermore, we show that Hermitian qubits can generate GHZ states with a high fidelity more than 0.9995 in a timescale comparable to that of non-Hermitian qubits, but at the expense of intense driving and large coupling constant. Our approach is scalable to a large number of qubits, presenting a promising pathway for advancing quantum technologies through the non-Hermiticity and higher-order exceptional points in many-body quantum systems.
arxiv pdf

Probing higher-order transitions through scattering of microwave photons in the ultrastrong-coupling regime of circuit QED

  1. Guan-Ting Chen,
  2. Po-Chen Kuo,
  3. Huan-Yu Ku,
  4. Guang-Yin Chen,
  5. and Yueh-Nan Chen
Higher-order transitions can occur in the ultrastrong-coupling regime of circuit QED through virtual processes governed by the counter-rotating interactions. We propose a feasible way
to probe higher-order transitions through the scattering of propagating microwave photons incident on the hybrid qubit-cavity system. The lineshapes in the scattering spectra can indicate the coherent interaction between the qubits and the cavity, and the higher-order transitions can be identified in the population spectra. We further find that if the coupling strengths between the two qubits and the cavity are tuned to be asymmetric, the dark antisymmetric state with the Fano-lineshape can also be detected from the variations in the scattering spectra.
arxiv pdf