Chang-Ling Zou

Magnon dark modes and gradient memory

  1. Xufeng Zhang,
  2. Chang-Ling Zou,
  3. Na Zhu,
  4. Florian Marquardt,
  5. Liang Jiang,
  6. and Hong X. Tang
Extensive efforts have been expended in developing hybrid quantum systems to overcome the short coherence time of superconducting circuits by introducing the naturally long-lived spin
degree of freedom. Among all the possible materials, single-crystal yttrium iron garnet has shown up very recently as a promising candidate for hybrid systems, and various highly coherent interactions, including strong and even ultra-strong coupling, have been demonstrated. One distinct advantage of these systems is that the spins are in the form of well-defined magnon modes, which allows flexible and precise tuning. Here we demonstrate that by dissipation engineering, a non-Markovian interaction dynamics between the magnon and the microwave cavity photon can be achieved. Such a process enables us to build a magnon gradient memory to store information in the magnon dark modes, which decouple from the microwave cavity and thus preserve a long life-time. Our findings provide a promising approach for developing long-lifetime, multimode quantum memories.
arxiv pdf

Universal Control of an Oscillator with Dispersive Coupling to a Qubit

  1. Stefan Krastanov,
  2. Victor V. Albert,
  3. Chao Shen,
  4. Chang-Ling Zou,
  5. Reinier W. Heeres,
  6. Brian Vlastakis,
  7. Robert J. Schoelkopf,
  8. and Liang Jiang
We investigate quantum control of an oscillator mode off-resonantly coupled to an ancillary qubit. In the strong dispersive regime, we may drive the qubit conditioned on number states
of the oscillator, which together with displacement operations can achieve universal control of the oscillator. Based on our proof of universal control, we provide explicit constructions for arbitrary state preparation and arbitrary unitary operation of the oscillator. Moreover, we present an efficient procedure to prepare the number state ∣∣n⟩ using only O(n‾‾√) operations. We also compare our scheme with known quantum control protocols for coupled qubit-oscillator systems. This universal control scheme of the oscillator can readily be implemented using superconducting circuits.
arxiv pdf