@article{Crognaletti2024,

title = {Equivariant Variational Quantum Eigensolver to detect phase transitions through energy level crossings},

author = {Giulio Crognaletti and Giovanni Di Bartolomeo and Michele Vischi and Luciano Loris Viteritti},

doi = {10.1088/2058-9565/ad9be3},

issn = {2058-9565},

year  = {2025},

date = {2025-01-01},

journal = {Quantum Sci. Technol.},

volume = {10},

number = {1},

publisher = {IOP Publishing},

abstract = {Abstract

               Level spectroscopy stands as a powerful method for identifying the transition point that delineates distinct quantum phases. Since each quantum phase exhibits a characteristic sequence of excited states, the crossing of energy levels between low-lying excited states offers a reliable mean to estimate the phase transition point. While approaches like the Variational Quantum Eigensolver are useful for approximating ground states of interacting systems using quantum computing, capturing low-energy excitations remains challenging. In our study, we introduce an equivariant quantum circuit that preserves the total spin and the translational symmetry to accurately describe singlet and triplet excited states in the J

                  1–J

                  2 Heisenberg model on a chain, which are crucial for characterizing its transition point. Additionally, we assess the impact of noise on the variational state, showing that conventional mitigation techniques like Zero Noise Extrapolation reliably restore its physical properties.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiBartolomeo2024b,

title = {Efficient quantum algorithm to simulate open systems through a single environmental qubit},

author = {Giovanni Di Bartolomeo and Michele Vischi and Tommaso Feri and Angelo Bassi and Sandro Donadi},

doi = {10.1103/physrevresearch.6.043321},

issn = {2643-1564},

year  = {2024},

date = {2024-12-00},

journal = {Phys. Rev. Research},

volume = {6},

number = {4},

publisher = {American Physical Society (APS)},

abstract = {We present an efficient algorithm for simulating open quantum systems dynamics described by the Lindblad master equation on quantum computers, addressing key challenges in the field. In contrast to existing approaches, our method achieves two significant advancements. First, we employ a repetition of unitary gates on a set of n system qubits and, remarkably, only a single ancillary bath qubit representing the environment. It follows that, for the typical case of m locality of the Lindblad operators, we reach an exponential improvement of the number of ancilla in terms of m and up to a polynomial improvement in ancilla overhead for large n with respect to other approaches. Although stochasticity is introduced, requiring multiple circuit realizations, the sampling overhead is independent of the system size. Second, we show that, under fixed accuracy conditions, our algorithm enables a reduction in the number of Trotter steps compared to other approaches, substantially decreasing circuit depth. These advancements hold particular significance for near-term quantum computers, where minimizing both width and depth is critical due to inherent noise in their dynamics.

          

            

            

              

                Published by the American Physical Society

                2024

              

            

          },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vischi2024,

title = {Simulating photonic devices with noisy optical elements},

author = {Michele Vischi and Giovanni Di Bartolomeo and Massimiliano Proietti and Seid Koudia and Filippo Cerocchi and Massimiliano Dispenza and Angelo Bassi},

doi = {10.1103/physrevresearch.6.033337},

issn = {2643-1564},

year  = {2024},

date = {2024-09-00},

journal = {Phys. Rev. Research},

volume = {6},

number = {3},

publisher = {American Physical Society (APS)},

abstract = {Quantum computers are inherently affected by noise. While in the long term, error correction codes will account for noise at the cost of increasing physical qubits, in the near term, the performance of any quantum algorithm should be tested and simulated in the presence of noise. As noise acts on the hardware, the classical simulation of a quantum algorithm should not be agnostic on the platform used for the computation. In this paper, we apply the recently proposed noisy gates approach to efficiently simulate noisy optical circuits described in the dual rail framework. The evolution of the state vector is simulated directly, without requiring the mapping to the density matrix framework. Notably, we test the method on both the gate-based and measurement-based quantum computing models, showing that the approach is very versatile. We also evaluate the performance of a photonic variational quantum algorithm to solve the MAX-2-CUT problem. In particular we design and simulate an ansatz, which is resilient to photon losses up to p∼10−3 making it relevant for near-term applications.

          

            

            

              

                Published by the American Physical Society

                2024

              

            

          },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiBartolomeo2024,

title = {Experimental bounds on linear-friction dissipative collapse models from levitated optomechanics},

author = {Giovanni Di Bartolomeo and Matteo Carlesso},

doi = {10.1088/1367-2630/ad3842},

issn = {1367-2630},

year  = {2024},

date = {2024-04-01},

journal = {New J. Phys.},

volume = {26},

number = {4},

publisher = {IOP Publishing},

abstract = {Abstract

               Collapse models constitute an alternative to quantum mechanics that solve the well-know quantum measurement problem. In this framework, a novel approach to include dissipation in collapse models has been recently proposed, and awaits experimental scrutiny. Our work establishes experimental bounds on the so-constructed linear-friction dissipative Diósi-Penrose (dDP) and Continuous Spontaneous localisation (dCSL) models by exploiting experiments in the field of levitated optomechanics. Our results in the dDP case exclude collapse temperatures below 10−13 K and 

                     

                     

                        

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                           ×

                           

                              10

                              

                                 −

                                 12

                              

                           

                        

                     

                     

                   K respectively for values of the localisation length smaller than 10−6 m and 10−8 m. In the dCSL case the entire parameter space is excluded for values of the temperature lower than 

                     

                     

                        

                           6

                           ×

                           

                              10

                              

                                 −

                                 9

                              

                           

                        

                     

                     

                   K.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiBartolomeo2023b,

title = {Noisy gates for simulating quantum computers},

author = {Giovanni Di Bartolomeo and Michele Vischi and Francesco Cesa and Roman Wixinger and Michele Grossi and Sandro Donadi and Angelo Bassi},

doi = {10.1103/physrevresearch.5.043210},

issn = {2643-1564},

year  = {2023},

date = {2023-12-00},

journal = {Phys. Rev. Research},

volume = {5},

number = {4},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiBartolomeo2023,

title = {Linear-friction many-body equation for dissipative spontaneous wave-function collapse},

author = {Giovanni Di Bartolomeo and Matteo Carlesso and Kristian Piscicchia and Catalina Curceanu and Maaneli Derakhshani and Lajos Diósi},

doi = {10.1103/physreva.108.012202},

issn = {2469-9934},

year  = {2023},

date = {2023-07-00},

journal = {Phys. Rev. A},

volume = {108},

number = {1},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DiBartolomeo2021,

title = {Gravity as a classical channel and its dissipative generalization},

author = {Giovanni Di Bartolomeo and Matteo Carlesso and Angelo Bassi},

doi = {10.1103/physrevd.104.104027},

issn = {2470-0029},

year  = {2021},

date = {2021-11-00},

journal = {Phys. Rev. D},

volume = {104},

number = {10},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}