RQMP (CPM) Seminar

Quantum Nonreciprocity with Nonlinearity and Weyl semimetals

Alex Krasnok

Florida International University

The emerging field of quantum computing has been rapidly growing and has shown interesting opportunities to overcome the limitations of classical computers for many currently unfeasible problems[1]. A key technology required for quantum computation devices is unidirectional signal propagation and routing, whereby electromagnetic radiation propagates asymmetrically between two points[2]. This effect is particularly important to protect JJ-qubits from reflections and noise originating in the readout. However, most modern nonreciprocal components are realized based on the magneto-optical effect in ferrite materials[3]. These devices are barely tunable, bulky, and incompatible with planar technologies, including transmission-line quantum circuits (circuit QED). Although isolators based on other approaches, e.g., two-dimensional magnetic materials and topological isolators/semimetals, cold atoms, have been extensively investigated recently, they are still limited in many aspects and unsuitable for superconducting circuit QED systems. Another recently extensively developed approach based on time-modulated isolators requires precise control over the modulation phase and connection to the external modulation generators and hence is also subject to thermal and apparate noise.

In this talk, I will present our recent results on isolators suitable for quantum systems. We will discuss the isolation effect obtained by a suitable combination of quantum nonlinearities and symmetry breaking[4]. By an example of a two-qubit system, we show that the presence of the dark state[5] is crucial to establishing strong nonreciprocity in this class of systems. Such two-qubit devices have been implemented as systems with an asymmetric dependence on the direction of the input field, allowing them to act like unidirectional devices in circuit QED. Then we will discuss how the circuit with Lorentz-type qubits can be turned into Fano-type qubits with the asymmetric spectral response, which improves the isolator figure of merit, power bandwidth, and efficiency. Finally, we will discuss a novel approach to tunable isolation based on twisted bilayered Weyl semimetals. The approach enables highly efficient tuning of both direction and value of isolation with the relative rotation of Weyl semimetals.

[1] E. Gibney, “Hello quantum world! Google publishes landmark quantum supremacy claim,” Nature, vol. 574, no. 7779, pp. 461–462, Oct. 2019, doi: 10.1038/d41586-019-03213-z.
[2] S. V. Kutsaev, A. Krasnok, S. N. Romanenko, A. Y. Smirnov, K. Taletski, and V. P. Yakovlev, “Up‐And‐Coming Advances in Optical and Microwave Nonreciprocity: From Classical to Quantum Realm,” Adv. Photonics Res., vol. 2, no. 3, p. 2000104, Mar. 2021, doi: 10.1002/adpr.202000104.
[3] D. M. Pozar, Microwave engineering, 4th Edition. John Wiley & Sons, Inc., 2011.
[4] N. Nefedkin, M. Cotrufo, A. Krasnok, and A. Alù, “Dark-State Induced Quantum Nonreciprocity,” Adv. Quantum Technol., vol. 5, no. 3, p. 2100112, Mar. 2022, doi: 10.1002/qute.202100112.
[5] N. Nefedkin, A. Alù, and A. Krasnok, “Quantum Embedded Superstates,” Adv. Quantum Technol., vol. 4, no. 6, p. 2000121, Jun. 2021, doi: 10.1002/qute.202000121.