Chao Shen

Quantum Channel Construction with Circuit Quantum Electrodynamics

  1. Chao Shen,
  2. Kyungjoo Noh,
  3. Victor V. Albert,
  4. Stefan Krastanov,
  5. Michel H. Devoret,
  6. Robert J. Schoelkopf,
  7. S. M. Girvin,
  8. and Liang Jiang
Quantum channels can describe all transformations allowed by quantum mechanics. We provide an explicit universal protocol to construct all possible quantum channels, using a single
qubit ancilla with quantum non-demolition readout and adaptive control. Our construction is efficient in both physical resources and circuit depth, and can be demonstrated using superconducting circuits and various other physical platforms. There are many applications of quantum channel construction, including system stabilization and quantum error correction, Markovian and exotic channel simulation, implementation of generalized quantum measurements and more general quantum instruments. Efficient construction of arbitrary quantum channels opens up exciting new possibilities for quantum control, quantum sensing and information processing tasks.
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