Publications by Department of Quantum Information

@article{Minganti2021b,
title = {Continuous dissipative phase transitions with or without symmetry breaking},
author = {Fabrizio Minganti and Ievgen I Arkhipov and Adam Miranowicz and Franco Nori},
url = {https://doi.org/10.1088/1367-2630/ac3db8},
doi = {10.1088/1367-2630/ac3db8},
year = {2021},
date = {2021-12-22},
journal = {New Journal of Physics},
volume = {23},
number = {12},
pages = {122001},
publisher = {IOP Publishing},
abstract = {The paradigm of second-order phase transitions (PTs) induced by spontaneous symmetry breaking (SSB) in thermal and quantum systems is a pillar of modern physics that has been fruitfully applied to out-of-equilibrium open quantum systems. Dissipative phase transitions (DPTs) of second order are often connected with SSB, in close analogy with well-known thermal second-order PTs in closed quantum and classical systems. That is, a second-order DPT should disappear by preventing the occurrence of SSB. Here, we prove this statement to be wrong, showing that, surprisingly, SSB is not a necessary condition for the occurrence of second-order DPTs in out-of-equilibrium open quantum systems. We analytically prove this result using the Liouvillian theory of DPTs, and demonstrate this anomalous transition in a paradigmatic laser model, where we can arbitrarily remove SSB while retaining criticality, and on a Z2-symmetric model of a two-photon Kerr resonator. This new type of PT cannot be interpreted as a ‘semiclassical’ bifurcation, because, after the DPT, the system steady state remains unique.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Minganti2021,
title = {Liouvillian spectral collapse in the Scully-Lamb laser model},
author = {Fabrizio Minganti and Ievgen I Arkhipov and Adam Miranowicz and Franco Nori},
url = {https://doi.org/10.1103/physrevresearch.3.043197},
doi = {10.1103/physrevresearch.3.043197},
year = {2021},
date = {2021-12-21},
journal = {Physical Review Research},
volume = {3},
number = {4},
pages = {043197},
publisher = {American Physical Society (APS)},
abstract = {Phase transitions of thermal systems and the laser threshold were first connected more than forty years ago. Despite the nonequilibrium nature of the laser, the Landau theory of thermal phase transitions, applied directly to the Scully-Lamb laser model (SLLM), indicates that the laser threshold is a second-order phase transition, associated with a U(1) spontaneous symmetry breaking (SSB). To capture the genuine nonequilibrium phase transition of the SLLM (i.e., a single-mode laser without a saturable absorber), here we employ a quantum theory of dissipative phase transitions. Our results confirm that the U(1) SSB can occur at the lasing threshold but, in contrast to the Landau theory and semiclassical approximation, they signal that the SLLM “fundamental” transition is a different phenomenon, which we call Liouvillian spectral collapse; that is, the emergence of diabolic points of infinite degeneracy. By considering a generalized SLLM with additional dephasing, we witness a second-order phase transition, with a Liouvillian spectral collapse, but in the absence of symmetry breaking. Most surprisingly, the phase transition corresponds to the emergence of dynamical multistability even without SSB. Normally, bistability is suppressed by quantum fluctuations, while in this case, the very presence of quantum fluctuations enables bistability. This rather anomalous bistability, characterizing the truly dissipative and quantum origin of lasing, can be an experimental signature of our predictions, and we show that it is associated with an emergent dynamical hysteresis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Jirakova2021b,
title = {Experimental hierarchy and optimal robustness of quantum correlations of two-qubit states with controllable white noise},
author = {Kate{ř}ina Jirákov á and Antonín Č and Karel Lemr and Karol Bartkiewicz and Adam Miranowicz},
url = {https://doi.org/10.1103/physreva.104.062436},
doi = {10.1103/physreva.104.062436},
year = {2021},
date = {2021-12-21},
journal = {Physical Review A},
volume = {104},
number = {6},
pages = {062436},
publisher = {American Physical Society (APS)},
abstract = {We demonstrate a hierarchy of various classes of quantum correlations on experimentally prepared two-qubit Werner-like states with controllable white noise. Werner states, which are white-noise-affected Bell states, are prototypal examples for studying such a hierarchy as a function of the amount of white noise. We experimentally generate Werner states and their generalizations, i.e., partially entangled pure states affected by white noise. These states enable us to study the hierarchy of the following classes of correlations: separability, entanglement, steering in three- and two-measurement scenarios, and Bell nonlocality. We show that the generalized Werner states (GWSs) reveal fundamentally different aspects of the hierarchy compared to the Werner states. In particular, we find five different parameter regimes of the GWSs, including those steerable in a two-measurement scenario but not violating Bell inequalities. This regime cannot be observed for the usual Werner states. Moreover, we find threshold curves separating different regimes of the quantum correlations and find the optimal states which allow for the largest amount of white noise which does not destroy their specific quantum correlations (e.g., unsteerable entanglement). Thus, we could identify the optimal Bell-nondiagonal GWSs which are, for this specific meaning, more robust against the white noise compared to the Bell-diagonal GWSs (i.e., Werner states).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Grudka2021,
title = {Quantum semipermeable barriers: Investigating Maxwell's demon toolbox},
author = {Andrzej Grudka and Paweł Kurzyński and Antoni Wójcik},
url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.104.064114},
doi = {10.1103/PhysRevE.104.064114},
year = {2021},
date = {2021-12-10},
journal = {Physical Review E},
volume = {104},
pages = {064114},
abstract = {We study quantum Maxwell's demon in a discrete space-time setup. We consider a collection of particles hopping on a one-dimensional chain and a semipermeable barrier that allows the particles to hop in only one direction. Our main result is a formulation of a local unitary dynamics describing the action of this barrier. Such dynamics utilizes an auxiliary system A and we study how properties of A influence the behavior of particles. An immediate consequence of unitarity is the fact that particles cannot be trapped on one side of the barrier forever, unless A is infinite. In addition, coherent superpositions and quantum correlations are affected once particles enter the confinement region. Finally, we show that initial superposition of A allows the barrier to act as a beam splitter.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Kurzyński2021,
title = {Weighted Bures length uncovers quantum state sensitivity},
author = {Paweł Kurzyński},
url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.104.L052202},
doi = {10.1103/PhysRevE.104.L052202},
year = {2021},
date = {2021-11-18},
journal = {Physical Review E},
volume = {104},
pages = {L052202},
abstract = {The unitarity of quantum evolutions implies that an overlap between two initial states does not change in time. This property is commonly believed to explain the apparent lack of state sensitivity in quantum theory, a feature that is prevailing in classical chaotic systems. However, classical state sensitivity is based on a distance between two trajectories in phase space which is a completely different mathematical concept than an overlap between two vectors in Hilbert space. It is possible that state sensitivity in quantum theory can be detected with the help of some special metric. Here we show that the recently introduced Weighted Bures length achieves this task. We numerically investigate a unitary cellular automaton of N interacting qubits and analyze how a single-qubit perturbation affects the evolution of WBL between the unperturbed and perturbed states. We observe a linear growth of WBL if the qubits are arranged into a cyclic graph and an exponential growth if they are arranged into a random bipartite graph.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Xu2021,
title = {Optomechanical dynamics in the PT- and broken-PT-symmetric regimes},
author = {Hai Xu and Deng-Gao Lai and Yi-Bing Qian and Bang-Pin Hou and Adam Miranowicz and Franco Nori},
url = {https://doi.org/10.1103/physreva.104.053518},
doi = {10.1103/physreva.104.053518},
year = {2021},
date = {2021-11-04},
journal = {Physical Review A},
volume = {104},
number = {5},
pages = {053518},
publisher = {American Physical Society (APS)},
abstract = {We theoretically study the dynamics of an optomechanical system, consisting of a passive optical mode and an active mechanical mode, in the PT- and broken-PT-symmetric regimes. By fully analytical treatments for the dynamics of the average displacement and particle numbers, we reveal the phase diagram under different conditions and the various regimes of both PT symmetry and stability of the system. We find that by appropriately tuning either mechanical gain or optomechanical coupling, both phase transitions of the PT symmetry and stability of the system can be flexibly controlled. As a result, the dynamical behaviors of the average displacement, photons, and phonons are radically changed in different regimes. The presented physical mechanism is general and this method can be extended to a general model of dissipative and amplified coupled systems. Our study shows that PT-symmetric optomechanical devices can serve as a powerful tool for the manipulation of mechanical motion, photons, and phonons.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Li2021,
title = {Vector optomechanical entanglement},
author = {Ying Li and Ya-Feng Jiao and Jing-Xue Liu and Adam Miranowicz and Yun-Lan Zuo and Le-Man Kuang and Hui Jing},
url = {https://doi.org/10.1515/nanoph-2021-0485},
doi = {10.1515/nanoph-2021-0485},
year = {2021},
date = {2021-11-02},
journal = {Nanophotonics},
volume = {11},
number = {1},
pages = {67--77},
abstract = {The polarizations of optical fields, besides field intensities, provide more degrees of freedom to manipulate coherent light–matter interactions. Here, we propose how to achieve a coherent switch of optomechanical entanglement in a polarized-light-driven cavity system. We show that by tuning the polarizations of the driving field, the effective optomechanical coupling can be well controlled and, as a result, quantum entanglement between the mechanical oscillator and the optical transverse electric mode can be coherently and reversibly switched to that between the same phonon mode and the optical transverse magnetic mode. This ability to switch optomechanical entanglement with such a vectorial device can be important for building a quantum network being capable of efficient quantum information interchanges between processing nodes and flying photons.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Lai2021,
title = {Significant enhancement in refrigeration and entanglement in auxiliary-cavity-assisted optomechanical systems},
author = {Deng-Gao Lai and Wei Qin and Bang-Pin Hou and Adam Miranowicz and Franco Nori},
url = {https://journals.aps.org/pra/abstract/10.1103/PhysRevA.104.043521},
doi = {10.1103/PhysRevA.104.043521},
year = {2021},
date = {2021-10-22},
journal = {Phys. Rev. A},
volume = {104},
pages = {043521},
abstract = {We propose how to achieve significantly enhanced quantum refrigeration and entanglement by coupling a pumped auxiliary cavity to an optomechanical cavity. We obtain both analytical and numerical results and find optimal-refrigeration and -entanglement conditions under the auxiliary-cavity-assisted (ACA) mechanism. Our method leads to a significant amplification in the net refrigeration rate and reveals that the ACA entanglement has a much stronger noise robustness in comparison with the unassisted case. By appropriately designing the ACA mechanism, an effective mechanical susceptibility can be well adjusted, and a genuine tripartite entanglement of cooling-cavity photons, auxiliary-cavity photons, and phonons can be generated. Specifically, we show that both optomechanical refrigeration and entanglement can be greatly enhanced for the blue-detuned driving of the auxiliary cavity but suppressed for the red-detuned case. Our work paves a way towards further quantum control of macroscopic mechanical systems and the enhancement and protection of fragile quantum resources.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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@article{Qin2021,
title = {Generating Long-Lived Macroscopically Distinct Superposition States in Atomic Ensembles},
author = {Wei Qin and Adam Miranowicz and Hui Jing and Franco Nori},
url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.093602},
doi = {10.1103/PhysRevLett.127.093602},
year = {2021},
date = {2021-08-23},
journal = {Phys. Rev. Lett.},
volume = {127},
pages = {093602},
abstract = {We propose to create and stabilize long-lived macroscopic quantum superposition states in atomic ensembles. We show that using a fully quantum parametric amplifier can cause the simultaneous decay of two atoms and, in turn, create stabilized atomic Schrödinger cat states. Remarkably, even with modest parameters these intracavity atomic cat states can have an extremely long lifetime, up to 4 orders of magnitude longer than that of intracavity photonic cat states under the same parameter conditions, reaching tens of milliseconds. This lifetime of atomic cat states is ultimately limited to several seconds by extremely weak spin relaxation and thermal noise. Our work opens up a new way toward the long-standing goal of generating large-size and long-lived cat states, with immediate interests both in fundamental studies and noise-immune quantum technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Markiewicz2021,
title = {Borromean states in discrete-time quantum walks},
author = {Marcin Markiewicz and Marcin Karczewski and Paweł Kurzyński},
url = {https://quantum-journal.org/papers/q-2021-08-16-523/},
doi = {10.22331/q-2021-08-16-523},
year = {2021},
date = {2021-08-16},
journal = {Quantum},
volume = {5},
pages = {523},
abstract = {In the right conditions, removing one particle from a multipartite bound state can make it fall apart. This feature, known as the "Borromean property", has been recently demonstrated experimentally in Efimov states. One could expect that such peculiar behavior should be linked with the presence of strong inter-particle correlations. However, any exploration of this connection is hindered by the complexity of the physical systems exhibiting the Borromean property. To overcome this problem, we introduce a simple dynamical toy model based on a discrete-time quantum walk of many interacting particles. We show that the particles described by it need to exhibit the Greenberger-Horne-Zeillinger (GHZ) entanglement to form Borromean bound states. As this type of entanglement is very prone to particle losses, our work demonstrates an intuitive link between correlations and Borromean properties of the system. Moreover, we discuss our findings in the context of the formation of composite particles.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{PhysRevA.104.012220,
title = {Nonclassical oscillations in pre- and post-selected quantum walks},
author = {Xiao-Xiao Chen and Zhe Meng and Jian Li and Jia-Zhi Yang and An-Ning Zhang and Tomasz Kopyciuk and Paweł Kurzyński},
url = {https://link.aps.org/doi/10.1103/PhysRevA.104.012220},
doi = {10.1103/PhysRevA.104.012220},
year = {2021},
date = {2021-07-28},
journal = {Phys. Rev. A},
volume = {104},
pages = {012220},
publisher = {American Physical Society},
abstract = {Quantum walks are counterparts of classical random walks. They spread faster, which can be exploited in
information processing tasks, and constitute a versatile simulation platform for many quantum systems. Yet,
some of their properties can be emulated with classical light. This raises a question: which aspects of the model
are truly nonclassical? We address it by carrying out a photonic experiment based on a pre- and post-selection paradox. The paradox implies that if somebody could choose to ask either if the particle is at position x = 0 at even time steps or at position x = d (d > 1) at odd time steps, the answer would be positive, no matter
the question asked. Therefore, the particle seems to undergo long distance oscillations despite the fact that the
model allows it to jump one position at a time. We translate this paradox into a Bell-like inequality and then into
a contextuality witness. Finally, we experimentally verify this witness up to eight standard deviations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Tulewicz2021,
title = {Large Voltage-Tunable Spin Valve Based on a Double Quantum Dot},
author = {Patrycja Tulewicz and Kacper Wrześniewski and Szabolcs Csonka and Ireneusz Weymann},
url = {https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.16.014029},
doi = {https://doi.org/10.1103/PhysRevApplied.16.014029},
year = {2021},
date = {2021-07-12},
journal = {Phys. Rev. Applied},
volume = {16},
pages = {014029},
abstract = {We study the spin-dependent transport properties of a spin valve based on a double quantum dot. Each quantum dot is assumed to be strongly coupled to its own ferromagnetic lead, while the coupling between the dots is relatively weak. The current flowing through the system is determined within perturbation theory in the hopping between the dots, whereas the spectrum of a quantum-dot–ferromagnetic-lead subsystem is determined by means of the numerical renormalization group method. The spin-dependent charge fluctuations between ferromagnets and quantum dots generate an effective exchange field, which splits the double-dot levels. Such a field can be controlled, separately for each quantum dot, by the gate voltages or by changing the magnetic configuration of the external leads. We demonstrate that the considered double-quantum-dot spin-valve setup exhibits enhanced magnetoresistive properties, including both normal and inverse tunnel magnetoresistance. We also show that this system allows for the generation of highly spin-polarized currents, which can be controlled by purely electrical means. The considered double quantum dot with ferromagnetic contacts can thus serve as an efficient voltage-tunable spin valve characterized by high output parameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Arkhipov2021b,
title = {Generating high-order quantum exceptional points in synthetic dimensions},
author = {Ievgen I Arkhipov and Fabrizio Minganti and Adam Miranowicz and Franco Nori},
url = {https://doi.org/10.1103/physreva.104.012205},
doi = {10.1103/physreva.104.012205},
year = {2021},
date = {2021-07-08},
journal = {Physical Review A},
volume = {104},
number = {1},
pages = {012205},
publisher = {American Physical Society (APS)},
abstract = {Recently, there has been intense research in proposing and developing various methods for constructing high-order exceptional points (EPs) in dissipative systems. These EPs can possess a number of intriguing properties related to, e.g., chiral transport and enhanced sensitivity. Previous proposals to realize non-Hermitian Hamiltonians (NHHs) with high-order EPs have been mainly based on either direct construction of spatial networks of coupled modes or utilization of synthetic dimensions, e.g., mapping of spatial lattices to time or photon-number space. Both methods rely on the construction of effective NHHs describing classical or postselected quantum fields, which neglect the effects of quantum jumps and which, thus, suffer from a scalability problem in the quantum regime, when the probability of quantum jumps increases with the number of excitations and dissipation rate. Here, by considering the full quantum dynamics of a quadratic Liouvillian superoperator, we introduce a simple and effective method for engineering NHHs with high-order quantum EPs, derived from evolution matrices of system operator moments. That is, by quantizing higher-order moments of system operators, e.g., of a quadratic two-mode system, the resulting evolution matrices can be interpreted as alternative NHHs describing, e.g., a spatial lattice of coupled resonators, where spatial sites are represented by high-order field moments in the synthetic space of field moments. Notably, such a mapping allows correct reproduction of the results of the Liouvillian dynamics, including quantum jumps. As an example, we consider a U(1)-symmetric quadratic Liouvillian describing a bimodal cavity with incoherent mode coupling, which can also possess anti−PT symmetry, whose field moment dynamics can be mapped to an NHH governing a spatial network of coupled resonators with high-order EPs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Bartkiewicz2021b,
title = {Accuracy of Entanglement Detection via Artificial Neural Networks and Human-Designed Entanglement Witnesses},
author = {Jan Roik and Karol Bartkiewicz and Antonín Černoch and Karel Lemr},
url = {https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.15.054006},
doi = {https://doi.org/10.1103/PhysRevApplied.15.054006},
year = {2021},
date = {2021-05-04},
journal = {Phys. Rev. Applied},
volume = {15},
pages = {054006},
abstract = {The detection of entangled states is essential in both fundamental and applied quantum physics. However, this task proves to be challenging, especially for general quantum states. One can execute full state tomography but this method is time demanding, especially in complex systems. Other approaches use entanglement witnesses: these methods tend to be less demanding but lack reliability. Here, we demonstrate that artificial neural networks (ANNs) provide a balance between the two approaches. In this paper, we make a comparison of ANN performance with witness-based methods for random general two-qubit quantum states without any prior information on the states. Furthermore, we apply our approach to a real experimental data set.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Bogdanov2021,
title = {Electron Microscopic Study of Interdiffusion in Equiatomic Fe-Ni Composite},
author = {V.V. Bogdanov and R.V. Vovk and S.V. Dukarov and M.V. Klislitsa and S.I. Petrushenko and V.N. Sukhov and G.Ya. Khadzhai and Y.L. Goulatis and S.R. Vovk and E.S. Gevorkyan and A. Feher and P. Kollar and J. Fuzer and Jolanta Natalia Latosińska},
doi = {10.12693/APhysPolA.139.62},
year = {2021},
date = {2021-01-15},
journal = {Acta Physica Polonica A},
volume = {139},
number = {1},
pages = {62},
abstract = {The paper presents a study of interdiffusion processes in a binary Fe-Ni system (obtained by electroconsolidation of nickel and iron powders) by X-ray energy dispersive spectroscopy. Well-separated regions of almost pure iron and nickel have been discovered. The content of nickel, estimated from the concentration dependence of the interdiffusion coefficient, which determines the kinetics of the homogenization process of the electroconsolidated Fe-Ni composite sample, was ~70 at.%. The value of the interdiffusion coefficient of the electroconsolidated Fe-Ni composite is significantly higher than that of the alloy of similar composition which probably results from the effect of spark plasma sintering technology (pressure and current along the same direction during consolidation) but also from a significant contribution of diffusion with mass transfer along the particle boundaries in the composite.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{PhysRevLett.126.023602,
title = {Shortcuts to Adiabaticity for the Quantum Rabi Model: Efficient Generation of Giant Entangled Cat States via Parametric Amplification},
author = {Ye-Hong Chen and Wei Qin and Xin Wang and Adam Miranowicz and Franco Nori},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.023602},
doi = {10.1103/PhysRevLett.126.023602},
year = {2021},
date = {2021-01-14},
journal = {Phys. Rev. Lett.},
volume = {126},
pages = {023602},
publisher = {American Physical Society},
abstract = {We propose a method for the fast generation of nonclassical ground states of the Rabi model in the ultrastrong and deep-strong coupling regimes via the shortcuts-to-adiabatic (STA) dynamics. The time-dependent quantum Rabi model is simulated by applying parametric amplification to the Jaynes-Cummings model. Using experimentally feasible parametric drive, this STA protocol can generate large-size Schrödinger cat states, through a process that is ∼10 times faster compared to adiabatic protocols. Such fast evolution increases the robustness of our protocol against dissipation. Our method enables one to freely design the parametric drive, so that the target state can be generated in the lab frame. A largely detuned light-matter coupling makes the protocol robust against imperfections of the operation times in experiments.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Kalaga2021,
title = {Violation of Leggett–Garg Inequalities in a Kerr-Type Chaotic System},
author = {Joanna K. Kalaga and Anna Kowalewska-Kudłaszyk and Mateusz Nowotarski and Wiesław Leoński},
url = {https://doi.org/10.3390/photonics8010020},
doi = {10.3390/photonics8010020},
year = {2021},
date = {2021-01-12},
journal = {Photonics},
volume = {8},
number = {1},
pages = {20},
publisher = {MDPI AG},
abstract = {We consider a quantum nonlinear Kerr-like oscillator externally pumped by a series of ultrashort coherent pulses to analyze the quantum time-correlations appearing while the system evolves. For that purpose, we examine the violation of the Leggett–Garg inequality.
We show how the character of such correlations changes when the system’s dynamics correspond to the regular and chaotic regions of its classical counterpart.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}