Research Lines

We work in quantum mechanics and its foundations: the measurement problem, the meaning of the wave function, entaglement and nonlocality, the quantum-to-classical transition, the relation between quantum theory and relativity/gravity. The major research lines are:

Foundations of Quantum Mechanics and Collapse Models

Quantum mechanics is undoubtedly a successful theory. Nevertheless, it is still puzzling the scientific community with its unsolved problems. Where does the border between the quantum (microscopic) and the classical (macroscopic) world lay? How can one reconcile quantum linearity with the lack of macroscopic superpositions? What is the role of the wave function? How does it collapse? These are only few of the open problems on the foundations of quantum mechanics.

The group is engaged in developing and testing models of spontaneous wave function collapse, which aim at giving a coherent answer to the questions above. After the seminal model by Ghirardi, Rimini, and Weber [1], several models describing the wave function collapse were developed in the following years [2]. The group is focused on two research directions: testing current collapse models, working in close contact with experimental physicists, and developing their extensions to dissipative and non-Markovian dynamics, and to the relativistic framework [3].

The experimental testing of collapse models in particular is giving important results, greatly reducing the allowed parameter space. λ is the collapse rate and rC is the correlation distance of the noise providing the collapse. Bounds come from a cold atom experiment [4], from x-ray emission from a Germanium sample [5], from millikelvin nanomechanical cantilever experiments [6], from gravitational wave detectors LISA Pathfinder, LIGO and AURIGA [7], from the spectrum excitations of fermion and phonons respectively [9], and from theoretical considerations [8].

Decoherence and Open Quantum Systems

Even in the most sophisticated experimental laboratories, quantum systems are unavoidably affected by the surrounding environment. Such an action can overtone the effects one desire to observe. Beside phenomena like dissipation and approach to thermal equilibrium, which are also present in classical systems, in the context of open quantum systems environmental decoherence plays the most significant role. This is indeed responsible for the loss of the quantum coherence and thus of the quantum traits of the system dynamics. To reduce the environmental action on the system, it is essential an accurate derivation and characterization of effective equations of motion embedding such effects.

The group works on modelling and quantifying these phenomena and, in liaison with experimental collaborators, aims at testing them. A recently developed model concerns gravitational decoherence [10], where gravity plays the role of the environment causing the loss of quantum coherence.

Interplay between Quantum Theory and Gravity

The conciliation of relativity and quantum theories has always been problematic. The reasons are mainly two. On the one side, quantum nonlocality (exemplified by the violation of Bell inequalities) creates a direct conflict with special relativistic requirements. On the other side, the unification of quantum and gravitational phenomena has not yet reached the desired goal. On top of this, one should not forget that existing relativistic quantum field theories are plagued by infinities. Crucial questions are still open: how can our world be nonlocal but at the same time be relativistic? Does gravity really need to be quantized? How is the gravitational field generated by a quantum superposition shaped? In recent years, several scientists have been proposing ideas which differ from the dominant view. The group is engaged in understanding the source of friction between quantum theory and relativity/gravity [11].

Noises modeling in quantum computing and error mitigation techniques

Quantum computers promise to offer new and faster tools to solve optimization problems, to expand artificial intelligence and to simulate more complex molecules and materials. However, current quantum computers are affected by noises, caused by their interaction with the surrounding environment, that alter their ideal working. The practical utility of quantum devices has to be accelerated by pairing the imperfect hardware with tailored noise characterization and simulation, along with error mitigation strategies, software techniques aiming at reducing as much as possible the impact of noises. The group has developed an open source software package to simulate noisy quantum circuits that outperforms the best developed and most widely used simulators [12]. The group is currently extending the functionalities of the package to implement error mitigation.

Quantum Algorithms

The idea that quantum computers could be utilized to simulate open quantum systems, i.e. systems interacting with an external environment, has gained increasing interest in recent years. These simulations are expected to have high impact because for many physical systems the presence of environmental noise is a resource rather than a problem. For example noise enables novel functionalities in bio-molecular systems. The interplay of coherent quantum dynamics and environmental noise has the potential to impart fundamental advantages in chemical reactions. The exponential complexity of such systems make quantum computers the ideal platform to simulate their behavior. The group has developed an efficient quantum algorithm for the simulation of open systems [13] and it is currently working on its application on a relevant use-case to be run on real quantum hardware.

Quantum Networks

Communications based on quantum principles are revolutionizing various aspects of modern technologies, ranging from encrypted data transmission to distributed computation. For instance, differently from current encryption schemes, quantum protocols can produce cryptographic keys which are provably secure: no attack would ever be able to violate the communication. These possibilities are unlocked by leveraging intrinsically quantum concepts, such as entanglement and the uncertainty principle; to achieve this, one must push the technology to the quantum realm, for instance by communicating via single photons (informally, single particles of light). The group works in strict collaboration with experimentalists at the edge of these technological frontiers, developing the theoretical tools behind them and contributing to realising this vision [14].

References:

[1] G.C. Ghirardi, A. Rimini, and T. Weber, Phys. Rev. D 34, 470 (1986).
[2] A. Bassi and G.C. Ghirardi, Phys. Rep. 379, 257 (2003); A. Bassi et al., Rev. Mod. Phys. 85, 471 (2013).
[3] J. Nobakht et al., Phys. Rev. A 98, 042109 (2018); M. Carlesso, L. Ferialdi, and A. Bassi, Eur. Phys. J. D, 72, 159 (2018).
[4] M. Bilardello, et al., Physica A 462, 764 (2016).
[5] K. Piscicchia et al.,Entropy 19(7), 319 (2017).
[6]A. Vinante et al., Phys. Rev. Lett. 116, 090402 (2016); A. Vinante et al., ibid. 119, 110401 (2017).
[7] M. Carlesso et al., Phys. Rev. D 94, 124036 (2016).
[8] M. Toros, G. Gasbarri, and A. Bassi, Phys. Lett. A 381, 3921 (2017).
[9] S.L. Adler et al., Phys. Rev. D 99, 103001 (2019); S. L. Adler and A. Vinante, Phys. Rev. A 97, 052119 (2018). M. Bahrami, ibid. 97, 052118 (2018).
[10] A. Bassi et al., Class. Quantum Grav. 34, 193002 (2017); M. Carlesso and A. Bassi, Phys. Lett. A, 380, 31-32 (2016).
[11] A. Bassi, Nat. Phys. 11, 626 (2015); G. Gasbarri et al., Phys. Rev. D 96, 104013 (2017).
[12] G. Di Bartolomeo et al., Phys. Rev. Research 5, 043210 (2023).
[13] G. Di Bartolomeo et al., arXiv:2311.10009.
[14] D. Ribezzo et al., Advanced Quantum Technologies 6, 2200061 (2023).

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