Research On Charging Theory Of Quantum Small System In Open Environment

Battery being a device with energy storage has several types,such as traditional leadacid batteries,lithium-ion batteries,solar cells,etc.,which have a wide range of applications including the fields of electronics,medical treatment,and control.It has become an important direction to explore how to improve battery capacity,charge and discharge power and storage time of energy.With the advancement of science and technology,various devices or systems have miniaturized.At present,the focused research has shifted from the traditional macro-scale system to the micro-scale quantum level of micro-nano and even smaller molecular atoms.At the same time,the effective manipulation of molecules,atoms and even single photosystems has been achieved experimentally.In this context,exploring a type of quantum system that can effectively store and extract energy,that is,quantum battery,has become an important research topic in the field of quantum science and technology.Compared with traditional battery,quantum effects,such as quantum coherence and quantum entanglement in quantum systems,are important characteristics distinguishing from the conventional battery.Therefore,exploring the effects of different quantum effects on the performance of quantum batteries and revealing their thermodynamic properties has become an important brunch in quantum battery.Recently,research on open quantum batteries has attracted extensive attention,but it still remains in the preliminary exploration.Especially,the research of battery charging under the non-equilibrium bath is worthy of indepth exploration.Based on this,the charging characteristics of single/double qubit systems as quantum batteries in a non-equilibrium coherent environment(auxiliary bath),within the framework of the collision model,are studied in our work.The effects of quantum coherence in the auxiliary bath and the coupling strength between the auxiliary bath and the system on battery performances,including the maximum extractable work,average charging power,charging efficiency and charging saturation,have been discussed at length.We find that under certain conditions,the charging performance of the quantum battery with the coherent auxiliary bath is signicantly better than that of quantum with thermal bath.The features have been exhibited as follows: 1)under the weak coupling strength of systemancillae,the quantum coherence in the coherent auxiliary bath can effectively enhance the capacity and charging efficiency of the quantum battery.2)under the relatively coupling,the battery is suitable for short-time fast charging scheme,i.e.,having a large average charging power for a short time.3)for the coherent auxiliary bath,the battery has the characteristic of energy backflow during the charging process,and the energy at the first peak under strong coupling can exceed the saturation energy.In addition,the charging performance of single-bit battery with two-qubit ancillae has also investigated in this paper.Similarly,the influence of the local phase difference,coherence magnitude and the coupling strength between the battery and the auxiliary unit on the maximum extractable work,charging stability and charging efficiency of the battery is analyzed.And,we show that several characteristics: 1)The local phase difference between the two atoms in the auxiliary unit could determine the performance of the battery together with the coherence magnitude and the coupling strength,and in the specic parameter area the coherent battery outperform the classical batteries,that is,the battery has greater efficiency and capacity;2)By increasing the phase difference,the energy backflow of quantum battery during the charging process can be effectively suppressed.Specically,when the local phase is reversed,the backflow effect of the battery is completely suppressed,and the battery can be monotonically charged.3)Taking the X-state of ancillae,we verify the effects of the squeezing coherences and heat-exchange coherences in the auxiliary unit on the battery charging performance,and show that only the heat-exchange coherences can effectively improve the maximum extractable work and charging efficiency of the battery.By the investigation of the charging scheme of a single/double qubit system in a non-equilibrium coherent environment,the effects of quantum coherence in non-equilibrium bath on the charging performance of quantum battery has been clearly demonstrated,and revealed that quantum coherence in the environment(including coherence magnitude and relative phase)can be regarded as a useful quantum resource or battery "fuel" to enhance the overall performance of the quantum battery.The study has furtherly deepened our understanding of the thermodynamic properties of quantum coherence,and might be significant for the design of high-performance quantum battery.