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arXiv:1703.05949 · Physical review. E

Measurement-induced operation of two-ion quantum heat machines

Suman Chand, Asoka Biswas

Published Mar 7, 2017• 43 citations
arXivHTMLPDF

Abstract

We show how one can implement a quantum heat machine by using two interacting trapped ions, in presence of a thermal bath. The electronic states of the ions act like a working substance, while the vibrational mode is modelled as the cold bath. The heat exchange with the cold bath is mimicked by the projective measurement of the electronic states. We show how such measurement in a suitable basis can lead to either a quantum heat engine or a refrigerator, which undergoes a quantum Otto cycle. The local magnetic field is adiabatically changed during the heat cycle. The performance of the heat machine depends upon the interaction strength between the ions, the magnetic fields, and the measurement cost. In our model, the coupling to the hot and the cold baths is never switched off in an alternative fashion during the heat cycle, unlike other existing proposals of quantum heat engines. This makes our proposal experimentally realizable using current tapped-ion technology.

DOI
10.1103/physreve.95.032111

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We show how one can implement a quantum heat machine by using two interacting trapped ions, in presence of a thermal bath. The electronic states of the ions act like a working substance, while the vibrational mode is modelled as the cold bath. The heat exchange with the cold bath is mimicked by the projective measurement of the electronic states. We show how such measurement in a suitable basis can lead to either a quantum heat engine or a refrigerator, which undergoes a quantum Otto cycle. The local magnetic field is adiabatically changed during the heat cycle. The performance of the heat machine depends upon the interaction strength between the ions, the magnetic fields, and the measurement cost. In our model, the coupling to the hot and the cold baths is never switched off in an alternative fashion during the heat cycle, unlike other existing proposals of quantum heat engines. This makes our proposal experimentally realizable using current tapped-ion technology.
We demonstrate how the reciprocating heat cycle of a quantum Otto engine (QOE) can be implemented using a single ion and an always-on thermal environment. The internal degree of freedom of the ion is chosen as the working fluid, while the motional degree of freedom can be used as the cold bath. We show, that by adiabatically changing the local magnetic field, the work efficiency can be asymptotically made unity. We propose a projective measurement of the internal state of the ion that mimics the release of heat from the working fluid during the engine cycle. In our proposal, the coupling to the hot and the cold baths need not be switched off and on in an alternate fashion during the engine cycle, unlike other existing proposals of QOE. This renders the proposal experimentally feasible using the available tapped-ion engineering technology.
We study how a quantum heat engine based on a single trapped ion performs in finite time. The always-on thermal environment acts like the hot bath, while the motional degree of freedom of the ion plays the role of the effective cold bath. The hot isochoric stroke is implemented via the interaction of the ion with its hot environment, while a projective measurement of the internal state of the ion is performed as an equivalent to the cold isochoric stroke. The expansion and compression strokes are implemented via suitable change in applied magnetic field. We study in detail how the finite duration of each stroke affects the engine performance. We show that partial thermalization can in fact enhance the efficiency of the engine, due to the residual coherence, whereas faster expansion and compression strokes increase the inner friction and therefore reduce the efficiency.
We investigate a quantum Otto engine (QOE) constructed from the two-qubit quantum Rabi model, operating within a cavity quantum electrodynamics (QED) architecture. The engine operates with two qubits as the working substance and a single non-Markovian hot thermal bath, modeled via the hierarchical equations of motion (HEOM) formalism. In place of a conventional cold thermal reservoir, the cooling stroke is realized through a projective measurement protocol on the cavity mode, which acts as an ancillary subsystem and effectively mimics a cold bath for the qubit working medium via measurement back-action. A squeezing drive applied to the cavity mode serves as a quantum fuel. We demonstrate that cavity squeezing systematically enhances both the power output and operational efficiency of the engine - the work extracted per unit of heat drawn from the hot bath-driving it above the standard quantum Otto limit. In the limit-cycle regime, the efficiency, while remaining above the Otto bound throughout, asymptotically converges to it from above. This identifies squeezing as a controllable quantum resource for thermodynamic optimization. Our results reveal that the interplay between qubit-cavity coupling, measurement-induced cooling, and non-equilibrium squeezing gives rise to a multi-resource thermodynamic architecture with performance characteristics inaccessible to conventional two-bath quantum Otto engines, thereby providing a concrete route toward experimentally realizable quantum heat engines in cavity QED platforms.
We present a quantum-heat engine model utilizing a dual spin-pair architecture, wherein an Otto-like cycle is implemented using a single heat bath. The conventional cold bath is replaced by a measurement protocol, enabling engine operation without the need for a second thermal reservoir. Unlike standard quantum-heat engines, our framework employs an ancillary spin pair in a two-dimensional configuration to regulate performance. Operating in finite time, the engine attains finite power, which is enhanced through quantum correlations, specifically correlation between spin pairs and projective measurements on the ancillary pair. The system consists of dual-qubit pairs, where one pair serves as the working medium and the other as an ancillary system facilitating measurement-induced heat exchange. We demonstrate that the engine efficiency can exceed the standard quantum Otto limit through local control of the ancillary pair while maintaining nonzero power output. Moreover, correlation between spin pairs enables efficiency modulation via the measurement basis, underscoring the role of quantum resources in optimizing quantum thermal machines.
Measurement-based quantum heat engines have attracted significant interest as alternatives to conventional thermal engines, as they replace the hot thermal reservoir with quantum measurements, thereby offering greater controllability and simpler implementation. Motivated by these advantages, we investigate a measurement-driven quantum Otto engine with a qubit working substance and study the optimal work extractable from such engines, including whether their performance can surpass that of conventional quantum Otto cycles. We analyze the engine in both the infinite-time (adiabatic) and finite-time (non-adiabatic) regimes, considering two distinct implementations obtained through optimization over all projection-valued measurements (PVMs) and over all two-outcome positive operator-valued measurements (POVMs). We show that measurement-based engines can outperform conventional quantum Otto engines within specific parameter regimes and that POVM-based engines can yield higher optimal work extraction than PVM-based ones. Furthermore, by incorporating the thermodynamic cost associated with resetting the auxiliary system required for POVM implementation, we demonstrate that the resulting net work output can still exceed that of PVM-based engines under suitable conditions on the spectral gaps and cold bath temperature. We also identify regimes in which non-adiabatic implementations can yield higher work output and efficiency than their adiabatic counterparts. Our study provides operational guidelines for designing improved measurement-driven quantum Otto engines.
We propose a thermodynamic cycle similar to the Otto cycle with a two-qubit working substance such that one of its isochoric strokes is provided by a controllable quantum measurement. We show that the measurement device can affect the working substance in four possible ways, as well as the energy exchanges between the working substance and an external work source during the isentropic strokes take place in two possible ways. By these considerations, we obtain eight thermal machines, each of which works individually in engine, accelerator, or refrigerator modes. We show that, for half of the obtained thermal machines, the applied quantum measurement causes their respective performances to go higher than the corresponding regular Otto limits, while the remainder go lower than the mentioned limits. Interestingly, it is shown that the performance of each thermal machine explicitly depends on the strength parameters of applied measurement, which in turn are related to coupling constants of the working substance and measurement device. These findings highlight that the role of generalized measurements as nonequilibrium quantum resources is not always constructive in powering the thermal machines.