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We present a detailed study of an asymmetrically driven quantum Otto engine with a time-dependent harmonic oscillator as its working medium. We obtain analytic expressions for the upper bounds on the efficiency of the engine for two different driving schemes having asymmetry in the expansion and compression work strokes. We show that the Otto cycle under consideration cannot operate as a heat engine in the low-temperature regime. Then, we show that the friction in the expansion stroke is significantly more detrimental to the performance of the engine as compared to the friction in the compression stroke. Further, by comparing the performance of the engine with sudden expansion, sudden compression, and both sudden strokes, we uncover a pattern of connections between the operational points, and we indicate the optimal operation regime for each case. Finally, we analytically characterize the complete phase diagram of the Otto cycle for both driving schemes and highlight the different operational modes of the cycle as a heat engine, refrigerator, accelerator, and heater.

Magnetocaloric materials have received significant attention of research community as they can minimize the use of harmful gases (CFCs, HFCs) and render eco-friendly refrigeration. Heusler alloys (Ni2MnGa) are known for their magnetocaloric effects, which make them useful as energy efficient and eco-friendly refrigerating materials. Magnetocaloric properties significantly depend on the composition of these alloys. Ni-Mn-Ga is one of the interesting Heusler systems, which exhibits magnetocaloric properties. In the present study, we performed the thermodynamic optimization of two sub binaries of the Ni-Mn-Ga system: Mn-Ga and Ni-Ga, using CALPHAD approach. A Modified Quasichemical Model (MQM) was used to describe the thermodynamic properties of the liquid solutions in both the binaries. Both the binaries were combined with Mn-Ni to develop a self-consistent thermodynamic database for Ni-Mn-Ga. In order to resolve the existing experimental discrepancies in the Mn-Ga and Ni-Ga system, few alloy compositions were prepared and analyzed using differential thermal analysis. Finally, the developed thermodynamic database was used to calculate the ternary isothermal section of the Ni-Mn-Ga (Heusler alloy) system at 1073 K with a proposed phase region for magnetocaloric applications., Comment: 26 Pages, 10 Figures

A bath with a negative temperature is a subject of intense debate in recent times. It raises fundamental questions not only on our understanding of negative temperature of a bath in connection with thermodynamics but also on the possibilities of constructing devices using such baths. In this work, we study steady-state quantum thermodynamics involving baths with negative temperatures. A bath with a negative temperature is created synthetically using two baths of positive temperatures and weakly coupling these with a qutrit system. These baths are then coupled to each other via a working system. At steady-state, the laws of thermodynamics are analyzed. We find that whenever the temperatures of these synthetic baths are identical, there is no heat flow, which reaffirms the zeroth law. There is always a spontaneous heat flow for different temperatures. In particular, heat flows from a bath with a negative temperature to a bath with a positive temperature which, in turn, implies that a bath with a negative temperature is `hotter' than a bath with a positive temperature. This warrants an amendment in the Kelvin-Planck statement of the second law, as suggested in earlier studies. In all these processes, the overall entropy production is positive, as required by the Clausius statement of the second law. We construct continuous heat engines operating between positive and negative temperature baths. These engines yield maximum possible heat-to-work conversion efficiency, that is, unity. We also study the thermodynamic nature of heat from a bath with a negative temperature and find that it is thermodynamic work but with negative entropy., Comment: 7+2 pages, comments welcome

We consider a micromaser model of a quantum battery, where the battery is a single mode of the electromagnetic field in a cavity, charged via repeated interactions with a stream of qubits, all prepared in the same non-equilibrium state, either incoherent or coherent, with the matter-field interaction modeled by the Jaynes-Cummings model. We show that the coherent protocol is superior to the incoherent one, in that an effective pure steady state is achieved for generic values of the model parameters. Finally, we supplement the above collision model with cavity losses, described by a Lindblad master equation. We show that battery performances, in terms of stored energy, charging power, and steady-state purity, are slightly degraded up to moderated dissipation rate. Our results show that micromasers are robust and reliable quantum batteries, thus making them a promising model for experimental implementations., Comment: 15 pages, 7 figures

We investigate the thermodynamic uncertainty relation (TUR), \textit{i.e.} a trade-off between entropy production rate and relative power fluctuations, for nondegenerate three-level and degenerate four-level maser heat engines. In the nondegenerate case, we consider two slightly different configurations of three-level maser heat engine and contrast their degree of violation of standard TUR. In the high-temperature limit, standard TUR relation is always violated for both configurations. We also uncover an invariance of TUR under simultaneous rescaling of the matter-field coupling constant and system-bath coupling constants. For the degenerate four level engine, we study the effects of noise-induced coherence on TUR. We show that depending on the parametric regime of operation, noise-induced coherence can either suppress or enhance the relative power fluctuations., Comment: 12 pages, 5 figures

We investigate the optimal performance of quantum Otto engine and refrigeration cycles of a time-dependent harmonic oscillator under a trade-off figure of merit for both adiabatic and nonadiabatic (sudden-switch) frequency modulations. For heat engine (refrigerator), the chosen trade-off figure of merit is an objective function defined by the product of efficiency (coefficient of performance) and work output (cooling load), thus representing a compromise between them. We obtain analytical expressions for the efficiency and coefficient of performance of the harmonic Otto cycle for the optimal performance of the thermal machine in various operational regimes. Particularly, in the sudden-switch regime, we discuss the implications of the nonadiabatic driving on the performance of the thermal machine under consideration, and obtain analytic expressions for the maximum achievable efficiency and coefficient of performance of the harmonic Otto thermal machine. Further, by carrying out a detailed comparative analysis of the heat engine operating under the chosen trade-off objective function with one operating at maximum work output, we show that the trade-off objective functions have desirable operation only for the adiabatic driving whereas for the sudden switch operation, the choice of a trade-off objective function does not make much difference as the performance of the engine is dominated by frictional effects., Comment: 11 pages, 5 figures

We show that a micromaser is an excellent model of quantum battery. A highly excited, pure, and effectively steady state of the cavity mode, charged by coherent qubits, can be achieved, also in the ultrastrong coupling regime of field-matter interaction. Stability of these appealing features against loss of coherence of the qubits and the effect of counter-rotating terms in the interaction Hamiltonian are also discussed., Comment: 6 pages, 1 figure

We investigate quantum Otto engine and refrigeration cycles of a time-dependent harmonic oscillator operating under the conditions of maximum $\Omega$-function, a trade-off objective function which represents a compromise between energy benefits and losses for a specific job, for both adiabatic and nonadiabatic (sudden) frequency modulations. We derive analytical expressions for the efficiency and coefficient of performance of the Otto cycle. For the case of adiabatic driving, we point out that in the low-temperature regime, the harmonic Otto engine (refrigerator) can be mapped to Feynman's ratchet and pawl model which is a steady state classical heat engine. For the sudden switch of frequencies, we obtain loop-like behavior of the efficiency-work curve, which is characteristic of irreversible heat engines. Finally, we discuss the behavior of cooling power at maximum $\Omega$-function and indicate the optimal operational point of the refrigerator., Comment: 9 pages, 5 figures, comments are welcome

In this work, We combined fully atomistic molecular dynamics and finite elements simulations with mechanical testings to investigate the mechanical behavior of atomic and 3D-printed models of pentadiamond. Pentadiamond is a recently proposed new carbon allotrope, which is composed of a covalent network of pentagonal rings. Our results showed that the stress-strain behavior is almost scale-independent. The stress-strain curves of the 3D-printed structures exhibit three characteristic regions. For low-strain values, this first region presents a non-linear behavior close to zero, followed by a well-defined linear behavior. The second regime is a quasi-plastic one and the third one is densification followed by structural failures (fracture). The Young's modulus values decrease with the number of pores. The deformation mechanism is bending-dominated and different from the layer-by-layer deformation mechanism observed for other 3D-printed structures. They exhibit good energy absorption capabilities, with some structures even outperforming kevlar. Interestingly, considering the Ashby chart, 3D-printed pentadiamond lies almost on the ideal stretch and bending-dominated lines, making them promising materials for energy absorption applications.

We study the optimal performance of a three-level quantum refrigerator using a trade-off objective function, $\Omega$ function, which represents a compromise between the energy benefits and the energy losses of a thermal device. First, we optimize the performance of our refrigerator by employing a two-parameter optimization scheme and show that the first two-terms in the series expansion of the obtained coefficient of performance (COP) match with those of some classical models of refrigerator. Then, in the high-temperature limit, optimizing with respect to one parameter while constraining the other one, we obtain the lower and upper bounds on the COP for both strong as well as weak (intermediate) matter-field coupling conditions. In the strong matter-field coupling regime, the obtained bounds on the COP exactly match with the bounds already known for some models of classical refrigerators. Further for weak matter-field coupling, we derive some new bounds on the the COP of the refrigerator which lie beyond the range covered by bounds obtained for strong matter-field coupling. Finally, in the parameter regime where both cooling power and $\Omega$ function can be maximized, we compare the cooling power of the quantum refrigerator at maximum $\Omega$ function with the maximum cooling power., Comment: 9 pages, 4 figures

We analyze the performance of a quantum Otto cycle, employing time-dependent harmonic oscillator as the working fluid undergoing sudden expansion and compression strokes during the adiabatic stages, coupled to a squeezed reservoir. First, we show that the maximum efficiency that our engine can achieve is 1/2 only, which is in contrast with the earlier studies claiming unit efficiency under the effect of squeezed reservoir. Then, we obtain analytic expressions for the upper bound on the efficiency as well as on the coefficient of performance of the Otto cycle. The obtained bounds are independent of the parameters of the system and depends on the reservoir parameters only. Additionally, with hot squeezed thermal bath, we obtain analytic expression for the efficiency at maximum work which satisfies the derived upper bound. Further, in the presence of squeezing in the cold reservoir, we specify an operational regime for the Otto refrigerator otherwise forbidden in the standard case., Comment: 6 Pages, 3 figures, Comments are welcome

We present a detailed study of a three-level quantum heat engine operating at maximum efficient power function, a trade-off objective function defined by the product of the efficiency and power output of the engine. First, for near equilibrium conditions, we find general expression for the efficiency and establish universal nature of efficiency at maximum power and maximum efficient power. Then in the high temperature limit, optimizing with respect to one parameter while constraining the other one, we obtain the lower and upper bounds on the efficiency for both strong as well as weak matter-field coupling conditions. Except for the weak matter-field coupling condition, the obtained bounds on the efficiency exactly match with the bounds already known for some models of classical heat engines. Further for weak matter-field coupling, we derive some new bounds on the the efficiency of the the engine which lie beyond the range covered by bounds obtained for strong matter-field coupling. We conclude by comparing the performance of our three-level quantum heat engine in maximum power and maximum efficient power regimes and show that the engine operating at maximum efficient power produces at least $88.89\%$ of the maximum power output while considerably reducing the power loss due to entropy production.

Over the ages, efforts have been made to use composite design to reinforce metals and alloys in order to increase their strength and modulus. On the other hand, nature herself improves the strength, ductility, stiffness and toughness of materials by strengthening them with liquids having zero strength/modulus. Here, emulating nature, efforts have been made to develop a new class of tin based alloy/composite with liquid metal reinforcement (LMM). Based on thermodynamic calculations, a composition has been designed such that on melting and casting it forms a solid metal (tin solid solution) and the eutectic mixture remains in liquid form at room temperature. The composite structure named as LMM shows multifold improvement in hardness, strength, ductility, toughness and wear resistance as compared to conventional solder alloys. A Finite Element Method (FEM) based simulation shows strain distribution in the composite which results in the unique behavior. The LMM also shows a negative coefficient of thermal expansion which is further verified using in-situ microscopy and thermodynamic calculations.

We study the optimal performance of a three-level quantum refrigerator using two different objective functions: cooling power and $\chi$-function. For both cases, we obtain general expressions for the coefficient of performance (COP) and derive its well-known lower and upper bounds for the limiting cases when the ratio of system-bath coupling constants at the hot and cold contacts approaches infinity and zero, respectively. We also show that the cooling power is optimizable only in the local region with respect to one control frequency, while $\chi$-function can be optimized globally with respect to two control frequencies. Additionally, we show that in the low-temperatures regime, our model of refrigerator can be mapped to Feynman's ratchet and pawl model, a classical mesoscopic heat engine. In the parameter regime where both cooling power and $\chi$-function can be optimized, we compare the cooling power of the quantum refrigerator at maximum $\chi$-function with the optimum cooling power., Comment: 9 pages, RevTex, two-column format, 5 Figures, 1 Table

Although classical and quantum heat engines work on entirely different fundamental principles, there is an underlying similarity. For instance, the form of efficiency at optimal performance may be similar for both types of engines. In this work, we study a three-level laser quantum heat engine operating at maximum ecological function (EF) which represents a compromise between the power output and the loss of power due to entropy production. We derive analytic expressions for efficiency under the assumptions of strong matter-field coupling and high bath temperatures. Upper and lower bounds on the efficiency exist in case of extreme asymmetric dissipation when the ratio of system-bath coupling constants at the hot and the cold contacts respectively approaches, zero or infinity. These bounds have been established previously for various classical models of Carnot-like engines. We conclude that while the engine produces at least 75\% of the power output as compared with the maximum power conditions, the fractional loss of power is appreciably low in case of the engine operating at maximum EF, thus making this objective function relevant from an environmental point of view., Comment: 9 pages, 5 figures

We study the optimal performance of Carnot-like heat engines working in low dissipation regime using the product of the efficiency and the power output, also known as the efficient power, as our objective function. Efficient power function represents the best trade-off between power and efficiency of a heat engine. We find lower and upper bounds on the efficiency in case of extreme asymmetric dissipation when the ratio of dissipation coefficients at the cold and the hot contacts approaches, respectively, zero or infinity. In addition, we obtain the form of efficiency for the case of symmetric dissipation. We also discuss the universal features of efficiency at maximum efficient power and derive the bounds on the efficiency using global linear-irreversible framework introduced recently by one of the authors., Comment: revtex4-1, 13 pages, 2 figures

Feynman's ratchet and pawl is a paradigmatic model for energy conversion using thermal fluctuations in the mesoscopic regime. Here, we optimize the power output of the ratchet as a heat engine in the high temperatures limit, and derive the universality of efficiency at maximum power up to second order, using a non-linear approximation. On the other hand, the linear model may be optimized by constraining the internal energy scales in different ways. It is shown that simple constraints lead to well-known expressions of thermal efficiency in finite-time thermodynamics. Thereby, the constrained ratchet, in the linear regime, has been mapped to an effective finite-time thermodynamic model., Comment: 12 pages, 4 figures