Franco Nori

A hybrid quantum circuit consisting of a superconducting flux qubit coupled to both a spin ensemble and a transmission-line resonator

  1. Ze-Liang Xiang,
  2. Xin-You Lu,
  3. Tie-Fu Li,
  4. J. Q. You,
  5. and Franco Nori
We propose an experimentally realizable hybrid quantum circuit for achieving a strong coupling between a spin ensemble and a transmission-line resonator via a superconducting flux qubit
used as a data bus. The resulting coupling can be used to transfer quantum information between the spin ensemble and the resonator. More importantly, in contrast to the direct coupling without a data bus, our approach requires far less spins to achieve a strong coupling between the spin ensemble and the resonator (e.g., 3 to 4 orders of magnitude less). This drastic reduction of the number of spins in the ensemble can greatly improve the quantum coherence of the spin ensemble. This proposed hybrid quantum circuit could enable a long-time quantum memory when storing information in the spin ensemble.
arxiv pdf

Hybrid quantum circuits: Superconducting circuits interacting with other quantum systems

  1. Ze-Liang Xiang,
  2. Sahel Ashhab,
  3. J. Q. You,
  4. and Franco Nori
Hybrid quantum circuits combine two or more physical systems, with the goal of harnessing the advantages and strengths of the different systems in order to better explore new phenomena
and potentially bring about novel quantum technologies. This article presents a brief overview of the progress achieved so far in the field of hybrid circuits involving atoms, spins and solid-state devices (including superconducting and nanomechanical systems). We discuss how these circuits combine elements from atomic physics, quantum optics, condensed matter physics, and nanoscience, and we present different possible approaches for integrating various systems into a single circuit. In particular, hybrid quantum circuits can be fabricated on a chip, facilitating their future scalability, which is crucial for building future quantum technologies, including quantum detectors, simulators and computers.
arxiv pdf

From blockade to transparency: controllable photon transmission through a circuit QED system

  1. Yu-xi Liu,
  2. Xun-Wei Xu,
  3. Adam Miranowicz,
  4. and Franco Nori
A strong photon-photon nonlinear interaction is a necessary condition for photon blockade. Moreover, this nonlinearity can also result a bistable behavior in the cavity field. We analyze
the relation between detecting field and photon blockade in a superconducting circuit QED system, and show that the photon blockade cannot occur when the detecting field is in the bistable regime. We further demonstrate that the photon transmission through such system can be controlled (from photon blockade to transparency) by the detecting field. Numerical simulations show that our proposal is experimentally realizable with current technology.
arxiv pdf

Implementing general measurements on linear optical and solid-state qubits

  1. Yukihiro Ota,
  2. Sahel Ashhab,
  3. and Franco Nori
We show a systematic construction for implementing general measurements on a single qubit, including both strong (or projection) and weak measurements. We mainly focus on linear optical
qubits. The present approach is composed of simple and feasible elements, i.e., beam splitters, wave plates, and polarizing beam splitters. We show how the parameters characterizing the measurement operators are controlled by the linear optical elements. We also propose a method for the implementation of general measurements in solid-state qubits.
arxiv pdf