arXiv subjects

P. G. Di Stefano

Publications and source records attributed to P. G. Di Stefano.

6 recordsLinked to original sources

arXiv2019

Ultrastrong coupling probed by Coherent Population Transfer

Light-matter interaction, and the understanding of the fundamental physics behind, is the scenario of emerging quantum technologies. Solid state devices allow the exploration of new regimes where ultrastrong coupling (USC) strengths are comparable to subsystem energies, and new exotic phenomena like quantum phase transitions and ground-state entanglement occur. While experiments so far provided only spectroscopic evidence of USC, we propose a new dynamical protocol for detecting virtual photon pairs in the dressed eigenstates. This is the fingerprint of the violated conservation of the number of excitations, which heralds the symmetry broken by USC. We show that in flux-based superconducting architectures this photon production channel can be coherenly amplified by Stimulated Raman Adiabatic Passage (STIRAP). This provides a unique tool for an unambiguous dynamical detection of USC in present day hardware. Implementing this protocol would provide a benchmark for control of the dynamics of USC architectures, in view of applications to quantum information and microwave quantum photonics.

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arXiv2018

Non-equilibrium thermodynamics of continuously measured quantum systems: a circuit-QED implementation

We propose a fully operational framework to study the non-equilibrium thermodynamics of a quantum system $S$ that is coupled to a detector $D$ whose state is continuously monitored, allowing to single out individual quantum trajectories of $S$. We focus on detailed fluctuation theorems and characterize the entropy production of the system. We establish fundamental differences with respect to the thermodynamic of unmonitored, unitarily evolved systems. We consider the paradigmatic example of circuit-QED, where superconducting qubits can be coupled to a continuously monitored resonator and show numerical simulations using state of the art experimental parameters.

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arXiv2017

Advances in quantum control of three-level superconducting circuit architectures

Advanced control in Lambda ($Λ$) scheme of a solid state architecture of artificial atoms and quantized modes would allow the translation to the solid-state realm of a whole class of phenomena from quantum optics, thus exploiting new physics emerging in larger integrated quantum networks and for stronger couplings. However control solid-state devices has constraints coming from selection rules, due to symmetries which on the other hand yield protection from decoherence, and from design issues, for instance that coupling to microwave cavities is not directly switchable. We present two new schemes for the $Λ$-STIRAP control problem with the constraint of one or two classical driving fields being always-on. We show how these protocols are converted to apply to circuit-QED architectures. We finally illustrate an application to coherent spectroscopy of the so called ultrastrong atom-cavity coupling regime.

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arXiv2016

Coherent manipulation of noise-protected superconducting artificial atoms in the Lambda scheme

We propose a new protocol for thr manipulation of a three-level artificial atom in Lambda ($Λ$) configuration in the absence of a direct pump coupling. It allows faithful, selective and robust population transfer analogous to stimulated Raman adiabatic passage ($Λ$-STIRAP), in highly noise protected superconducting artificial atoms. It combines the use of a two-photon pump pulse with suitable advanced control, operated by a slow modulation of the phase of the external fields, leveraging on the stability of semiclassical microwave drives. This protocol is a building block for novel tasks in complex quantum architectures. Its demonstration would be a benchmark for the implementation of a class of multilevel advanced control procedures for quantum computation and microwave quantum photonics in systems based on artificial atoms.

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arXiv2015

Population transfer in a Lambda system induced by detunings

In this paper we propose a new protocol to achieve coherent population transfer between two states in a three-level atom by using two ac fields. It is based on the physics of Stimulated Raman Adiabatic Passage (STIRAP), but it is implemented with the constraint of a reduced control, namely one of the fields cannot be switched off. A combination of frequency chirps is used with resonant fields, allowing to achieve approximate destructive interference, despite of the fact that an exact dark state does not exist. This new chirped STIRAP protocol is tailored for applications to artificial atoms, where architectures with several elementary units can be strongly coupled but where the possibility of switching on and off such couplings is often very limited. Demonstration of this protocol would be a benchmark for the implementation of a class of multilevel advanced control procedures for quantum computation and microwave quantum photonics in artificial atoms.

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arXiv2015

Design of a Lambda configuration in artificial coherent nanostructures

The implementation of a three-level Lambda System in artificial atoms would allow to perform advanced control tasks typical of quantum optics in the solid state realm, with photons in the $\mathrm{μm}$/mm range. However hardware constraints put an obstacle since protection from decoherence is often conflicting with efficient coupling to external fields. We address the problem of performing conventional STImulated Raman Adiabatic Passage (STIRAP) in the presence of low-frequency noise. We propose two strategies to defeat decoherence, based on "optimal symmetry breaking" and dynamical decoupling. We suggest how to apply to the different implementations of superconducting artificial atoms, stressing the key role of non-Markovianity.

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