P. Morfin

Over the past decade, autonomous stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schrödinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended nonlinear interactions. In this work, we leverage a genuine six-wave mixing process enabled by a near Kerr-free Josephson element to enforce dissipation of quartets of excitations in a high-impedance superconducting resonator. Owing to residual nonlinearities stemming from stray inductances in our circuit, this dissipation channel is only effective when the resonator holds a specific number of photons. Applying it to the fourth excited state of the resonator, we show an order-of-magnitude enhancement of the state decay rate while only marginally impacting the relaxation and coherence of lower-energy states. Given that stray inductances could be strongly reduced through simple modifications in circuit design and that our methods can be adapted to activate even higher-order dissipation channels, these results pave the way toward the dynamical stabilization of four-component Schrödinger cat qubits and even more complex bosonic qubits.

Spintronic terahertz emitters, based on optically triggered spin-to-charge conversion processes, have recently emerged as a novel route toward compact and efficient THz sources. The next challenge for technologically relevant devices, however, remains to modulate the emission with low-energy consumption during operation. In order to achieve this, ferroelectric materials coupled to active spin–orbit layers such as two-dimensional transition metal dichalcogenides are potential candidates. In this work, we present the realization of a large area heterostructure of CoFeB/PtSe2/MoSe2 on a macroscopically bidomain LiNbO3 substrate. Using THz time-domain spectroscopy, we show that the ferroelectric polarization direction induces a sizable modulation of the THz emission. We rationalize these experimental results by using band structure and spin accumulation calculations that are consistent with an interfacial spin-to-charge conversion mediated by the inverse Rashba–Edelstein effect at the MoSe2/PtSe2 interface and being tuned by ferroelectricity in the adjacent LiNbO3 surface. This work demonstrates the relevance and technological potential of field effect spin–orbit architectures for novel THz technologies.