Month: May 2024

Diving into the fascinating realm of quantum systems, the seminar will offer a panoramic view of long-range interactions. Starting with an encompassing tour of critical phenomena in systems featuring power-law interactions 1/𝑟𝛼 at 𝛼 < 𝑑, we’ll unveil the intricate equilibrium scaling dependence on the power-law exponent α. We will then take a deep dive into the dynamic world of “strong” long-range systems with 𝛼 < 𝑑, where we’ll unravel the counterintuitive features of out-of-equilibrium scaling dynamics during sudden and gradual quenches.

Zoom link: https://zoom.us/j/95634523890?pwd=N1QrSEpScG9lU3NrU1JCU3FVbDREZz09

Testing the limits of validity of the superposition principle is of crucial importance in the foundations of quantum mechanics and the development of quantum technologies. A way to quantify possible breakdowns of the superposition principle is given by collapse models. These models modify the Schrödinger equation, by adding non-linear and stochastic terms which describe spontaneous collapse in space of the wavefunction. The effects of the non-linear terms are negligible for microscopic systems however, because of an amplification mechanism built in the models, they become dominant for macroscopic objects, providing in this way a natural solution to the measurement problem. Because in collapse models the Schrödinger equation is modified, they make different predictions compared to Quantum Mechanics, hence they can be tested in experiments. We will introduce the most relevant collapse models, the Continuous Spontaneous Localization (CSL) model, and the Diósi-Penrose (DP) model. Then, we will give a summary of the current bounds set by different experiments on their phenomenological parameters. In particular, we will focus on experiments based on the study of radiation emission from matter.

The physical properties of many complex Quantum Materials (QM), like transition metal oxides, are the results of a complex interplay among electrons, phonons, and magnons. This complexity makes the properties of QM highly susceptible to external factors such as pressure, doping, magnetic fields, or temperature. This leads to the intricate phase diagrams found in many families of compounds and, in turn, provides the means to switch between completely different macroscopic functionalities by a fine tuneing of “control parameters”, such as temperature or pressure. The same susceptibility also renders QM an ideal platform for designing experiments where tailored electromagnetic fields interacting with matter can lead to the emergence on ultrafast timescales of novel, occasionally exotic, physical properties. This aspect has been explored in time domain studies [1] and has led to different proofs that ultrashort mid-IR light pulses can “force” the formation of quantum coherent states in matter. Those findings disclose a new regime of physics where photo- excitation can be used to dynamically “sustain” quantum coherence, thermodynamic-limits may be bridged and quantum effects can, in principle, appear at ambient temperatures, where thermal fluctuations normally inhibits them at equilibrium. In this presentation, I will review our recent results in archetypal strongly correlated cuprate superconductors and demonstrate the feasibility of a light-based control of quantum phases in real materials [2,3,4]. I will then introduce our new approaches to time domain spectroscopy going beyond mean photon number observables [5-10] and show that the statistical features of light can provide information on superconducting fluctuations beyond standard linear and non-linear optical spectroscopies [11]. Finally, I will elaborate on our current research effort to use cavity electrodynamics to control the onset of quantum coherent states in complex materials [12].

[1] Advances in physics 65, 58-238 (2016)

[2] Science 331, 189-191 (2011)

[3] Phys. Rev. Lett. 122, 067002 (2019)

[4] Nature Physics 17, 368–373 (2021)

[5] Phys. Rev. Lett. 119, 187403 (2017)

[6] New J. Phys. 16 043004 (2014)

[7] Nat. Comm. 6, 10249 (2015)

[8] PNAS March 19, 116 (12) 5383-5386 (2019)

[9] J. of Physics B 53, 145502 (2019)

[10] Optics Letters 45, 3498 (2020)

[11] Light: Science & Applications 11, 44 (2022)

[12] Nature 622, 487–492 (2023)

https://zoom.us/j/99542736244?pwd=U1YwVVZTVWtOOXE3QjFJbWlrQ1AyQT09

In addition to the usual projective measurements, quantum mechanics allows for alternative ways to extract information from a quantum system. Some of these lead to a quasi-probability distribution for the observable measured which are not positively defined. In perfect analogy with the Wigner quasiprobability distribution, the presence of negative regions in the distribution can be used to spot pure quantum behaviors of the system or the dynamics. I will present a particular scheme, called quantum non-demolition, where quasi-probability distribution arises naturally. It exploits an additional quantum detector coupled to the system to be measured which allows us to gain important information about the wave-function of the system. I will discuss what are the advantages and disadvantages of this approach with some practical examples: the measure of the work done on a quantum system driven by an external field and the calculation of the derivative of a quantum operator. In the last part of the talk, I will discuss the connection with the violation of the Leggett-Garg inequalities, and how this approach identifies pure quantum effects and quantum-to-classical transition due to the interaction with an environment.

https://zoom.us/j/91331596512?pwd=RFlwdTA5OTNYRmFaNGxjYUphclpFUT09