Small Open Systems Research Articles

Quantum computers, quantum computing, and quantum thermodynamics

Quantum thermodynamics aims to extend standard thermodynamics and non-equilibrium statistical physics to systems with sizes well below the thermodynamic limit. It is a rapidly evolving research field that promises to change our understanding of the foundations of physics, while enabling the discovery of novel thermodynamic techniques and applications at the nanoscale. Thermal management has turned into a major obstacle in pushing the limits of conventional digital computers and could also represent a crucial issue for quantum computers. The practical realization of quantum computers with superconducting loops requires working at cryogenic temperatures to eliminate thermal noise, and ion-trap qubits also need low temperatures to minimize collisional noise. In both cases, the sub-nanometric sizes also bring about the thermal broadening of the quantum states; and even room-temperature photonic computers eventually require cryogenic detectors. A number of thermal and thermodynamic questions, therefore, take center stage, such as quantum re-definitions of work and heat, thermalization and randomization of quantum states, the overlap of quantum and thermal fluctuations, and many others, even including a proper definition of temperature for the small open systems constantly out of equilibrium that are the qubits. This overview provides an introductory perspective on a selection of current trends in quantum thermodynamics and their impact on quantum computers and quantum computing, with language that is accessible to postgraduate students and researchers from different fields.

Rational Design of Memory‐Based Sensors: the Case of Molecular Calorimeters

AbstractThermodynamic characterization is crucial for understanding molecular interactions. However, methodologies for measuring heat changes in small open systems are extremely limited. We document a new approach for designing molecular sensors, that function as calorimeters: sensors based on memory. To design a memory‐based sensor, we take advantage of the unique kinetic properties of nucleic acid scaffolds. Particularly, we elaborate on the differences in folding and unfolding rates in nucleic acid quadruplexes. DNA‐based i‐motifs unfold fast in response to small heats but do not fold back when the system is equilibrated with surroundings. We translated this behavior into a molecular memory function that enables the measurement of heat changes in open environments. The new sensors are biocompatible, operate homogeneously, and measure small heats released over long time periods. As a proof‐of‐concept, we demonstrate how the molecular calorimeters report heat changes generated in water/propanol mixing and in ligand/protein binding.

Rational Design of Memory-Based Sensors: the Case of Molecular Calorimeters.

Thermodynamic characterization is crucial for understanding molecular interactions. However, methodologies for measuring heat changes in small open systems are extremely limited. We document a new approach for designing molecular sensors, that function as calorimeters: sensors based on memory. To design a memory-based sensor, we take advantage of the unique kinetic properties of nucleic acid scaffolds. Particularly, we elaborate on the differences in folding and unfolding rates in nucleic acid quadruplexes. DNA-based i-motifs unfold fast in response to small heats but do not fold back when the system is equilibrated with surroundings. We translated this behavior into a molecular memory function that enables the measurement of heat changes in open environments. The new sensors are biocompatible, operate homogeneously, and measure small heats released over long time periods. As a proof-of-concept, we demonstrate how the molecular calorimeters report heat changes generated in water/propanol mixing and in ligand/protein binding.

Entropy Production in Open Systems: The Predominant Role of Intraenvironment Correlations.

We show that the entropy production in small open systems coupled to environments made of extended baths is predominantly caused by the displacement of the environment from equilibrium rather than, as often assumed, the mutual information between the system and the environment. The latter contribution is strongly bounded from above by the Araki-Lieb inequality and therefore is not time extensive, in contrast to the entropy production itself. We confirm our results with exact numerical calculations of the system-environment dynamics.

Colloquium: Non-Markovian dynamics in open quantum systems

The dynamical behavior of open quantum systems plays a key role in many applications of quantum mechanics, examples ranging from fundamental problems, such as the environment-induced decay of quantum coherence and relaxation in many-body systems, to applications in condensed matter theory, quantum transport, quantum chemistry and quantum information. In close analogy to a classical Markov process, the interaction of an open quantum system with a noisy environment is often modelled by a dynamical semigroup with a generator in Lindblad form, which describes a memoryless dynamics leading to an irreversible loss of characteristic quantum features. However, in many applications open systems exhibit pronounced memory effects and a revival of genuine quantum properties such as quantum coherence and correlations. Here, recent results on the rich non-Markovian quantum dynamics of open systems are discussed, paying particular attention to the rigorous mathematical definition, to the physical interpretation and classification, as well as to the quantification of memory effects. The general theory is illustrated by a series of examples. The analysis reveals that memory effects of the open system dynamics reflect characteristic features of the environment which opens a new perspective for applications, namely to exploit a small open system as a quantum probe signifying nontrivial features of the environment it is interacting with. This article further explores the various physical sources of non-Markovian quantum dynamics, such as structured spectral densities, nonlocal correlations between environmental degrees of freedom and correlations in the initial system-environment state, in addition to developing schemes for their local detection. Recent experiments on the detection, quantification and control of non-Markovian quantum dynamics are also discussed.

Electron–phonon coupling in nanodevices

We study theoretically the manifestation of the nonadiabaticity of the electron–longitudinal optical (LO)-phonon small open system of a quantum dot. This nonadiabaticity has an influence on the current–voltage characteristics of the nanotransistor. The nanotransistor is represented by a semiconductor quantum dot with the attached source and the drain electrodes, together with a gate. Under a certain asymmetry of the contacts the electron–optical phonon interaction, causing the electronic states occupation upconversion, is shown to lead to a creation of a spontaneous voltage between the source and drain or, alternatively, to a spontaneous current in case when the source and the drain are shunted.

Fluctuation Induced Homochirality in an Open System

We study a possibility for chiral symmetry breaking to take place without autocatalytic process in an open system. Our model consists of an inflow of enantiomers and outflow of heterogeneous dimers from the system, which corresponds to the Frank model without autocatalysis. It is demonstrated analytically as well as numerically that the rate equations for this system does not predict any kind of symmetry breaking but the stochastic master equation predicts that the system approaches asymptotically a homochiral state. This is caused by the fluctuations induced by the discreteness of population numbers of enantiomers in their perpetual flow. It is argued that this scenario can be effective for a very small open system and could be a candidate for an initial chiral imbalance.

The equilibrium fluctuations in small open systems

The equilibrium distribution functions of momentum, energy, number of particles in small volumes of perfect gas are derived by methods of Gibbs statistical mechanics. The received expressions are checked up by the molecular dynamics method. Good agreement of the analytical formulas and the results of numerical simulation is revealed. Essential correlations of fluctuations of momentum and number of particles, of momentum and internal energy are observed.

A minimal duplex connection capability in the top three layers of the OSI reference model

A minimal duplex connection capability is described as the ability to open, close, abort, and transfer data through a duplex connection between two application processes. The goal of this paper is to describe a minimal duplex connection capability for the top three layers of the Open Systems Interconnection (OSI) Reference Model that will be appropriate for use by very small Open Systems such as home computers. Such a connection capability would allow these small systems to interconnect with machines of arbitrary size. The approach taken is to use only the parameters on service primitives that are absolutely required to accomplish this connection service. The protocol and services necessary to accomplish such a minimal connection are described for the application, presentation, and session layers of the OSI Reference Model. The existing draft proposals for services and protocol for the session layer provide a basis for this duplex connection service. A minor modification to the session draft proposals is suggested. The services for the presentation and application layer are defined in terms of the tentative service primitives being considered in the international standards efforts. The transparent initial context defined for the presentation layer is used to minimize the work of that layer. The benefits of this minimal duplex connection capability are then discussed from the point of view of very small Open Systems.