1 Introduction
Quantum batteries are quantum mechanical systems which are able to store or release energy and satisfy the requirement of miniature battery [
1,
2]. Currently widely used batteries are electrochemical devices [
3] that store energy into chemical energy and convert it into electrical energy to drive machines to work. As many electronic devices continue to be miniaturized to provide flexibility and portability [
4] and quantum technologies continue to make progress, it has become a prevalent topic to construct completely new energy storage devices called quantum batteries. They are based on quantum thermodynamics, which are fundamentally different from and transcend the traditional electrochemical batteries [
3]. The influences of quantum phenomena [
5–
13] such as coherence and entanglement on quantum batteries must be taken into account.
Since the introduction of quantum batteries in 2013 [
14], quantum phenomena have been used to improve the performances of the quantum batteries in various models [
15,
16], such as quantum cavity [
9,
17–
25], spin chain [
26–
32], Sachdev–Ye–Kitaev model [
33,
34], and quantum oscillators [
35–
38], showing quantum advantages. In the quantum cavity, a Dicke quantum battery is constructed by coupling
N two-level systems with a single photonic mode in a cavity [
18]. Interestingly, this collective charging protocol increases the charging power of a quantum battery by
times than the parallel one that assigns a single optical cavity to each two-level system [
17]. In fact, this collective quantum advantage that enhances the charging power of quantum batteries is widespread [
12]. Moreover, the charging power of a many-body quantum battery is further enhanced by considering the spin–spin interaction in the spin chain [
26]. The exactly solvable Sachdev–Ye–Kitaev model is also a suitable cell for describing quantum batteries, which has shown that the presence of non-local correlations can significantly inhibit the fluctuations of the average energy stored in quantum batteries [
34]. The quantum battery in quantum oscillators model consists of
N two-level atoms, and is charged through a harmonic charging field, which is significantly different from a static charging field. In the absence of interatomic interaction, it can be fully charged by appropriately adjusting driving frequency. The fully charging power can be further enhanced when repulsive interaction exists between large
N atoms [
35].
Recently, based on stimulated Raman adiabatic passage (STIRAP) technique, one propose a three-level quantum battery [
39,
40], which is a three-level system driven by two external optical or microwave fields that realizes the energy transfer between the ground state and the maximum excited state along the so-called dark state [
41–
43]. The characteristics of three-level systems that base on STIRAP to achieve quantum transitions have been studied in detail. For example, the loss due to spontaneous emission of the intermediate state is negligible, and the process is relatively insensitive to experimental imperfections in pulse intensity, shape and timing [
43]. These characteristics suppress undesired spontaneous discharging, and greatly enhance the stability and robustness of a three-level quantum battery charged by STIRAP [
39]. On that basis, it is shown that when an appropriate third driving field is applied to STIRAP, the transitions between the three quantum states can form a closed loop, which can effectively improve the charging power of the quantum battery [
40]. However, in order to maintain the system as closely as possible in the dark state, in general, it requires rather long time to satisfy adiabaticity.
The protocol of shortcuts to adiabaticity (STA) [
44,
45] is capable of accelerating the evolution in STIRAP and can be achieved by implementing an auxiliary field to suppress the nonadiabatic excitation in STIRAP. This method is also named counterdiabatic, transitionless or superadiabatic driving [
46–
51]. It has been widely used in atomic, molecular, optical and other fields [
45,
52,
53]. Experimentally, it has been implemented in superconducting circuit [
54], nitrogen–vacancy (N–V) centre [
55–
57], cold atoms [
58,
59], etc. Very recently, the transitionless driven quantum batteries, composed by a set of independent three-qubit cells are proposed and the energy resources can be further optimized by implementing the transitionless technique [
60].
In this paper, we investigate the characteristics of a three-level quantum battery when it is charged and discharged through STA. More specifically, based on counterdiabatic driving, we require an additional control field to ensure adiabaticity and form a three-level counterdiabatic STIRAP (cdSTIRAP) quantum battery. We are primarily concerned with the ergotropy which is the maximal energy can be extracted from the quantum battery to perform thermodynamic work [
24,
61–
65] and power of the quantum battery. We consider that the counterdiabatic protocol will enhance the charging and discharging power. To prove it, we study the properties of the cdSTIRAP quantum battery and compare them with STIRAP case. Meanwhile, we also simulate the effects of the amplitude and the delay time of driving fields on the charging process. Finally, we discuss the feasible schemes of our cdSTIRAP quantum battery in experiments.
The paper is organized as follows. In Section 2, we show a three-level quantum battery and charging (discharging) protocols. The Hamiltonian of the quantum battery involved in the corresponding protocol is introduced. Next in Section 3, we analyze the characteristics of the two charging protocols and calculated the corresponding maximum charging energy and average power. Then, the discharging processes are analyzed through STA in Section 4. We explore the feasible schemes of our cdSTIRAP quantum batteries in experiments in Section 5. Finally, a brief summary and discussion are reported in Section 6.
2 Model
In this section, we first briefly introduce the three-level quantum battery. The quantum battery Hamiltonian is . Here |i〉 are the energy eigenstate of a three-level system, and εi stand for the corresponding eigenenergies. The ground state |1〉 denotes a discharged battery. When the system is in the first excited state |2〉, it is similar to a partially charged quantum battery. And the system requires to be in the second excited state |3〉when the quantum battery is fully charged (see Fig. 1).
As shown in Fig. 1(a), the STIRAP charging or discharging protocol involves a P pulse on |1〉–|2〉 transition and a S pulse on |2〉–|3〉 transition. And the charging or discharging Hamiltonian under a time-dependent interaction picture reads [
39,
52,
55]
where is the reduced Planck constant (), and Ωp(t),Ωs(t) represent the amplitudes of the corresponding driving fields.
The three instantaneous eigenstates of Hamiltonian (1) are
and the corresponding eigenvalues are
λ− = −Ω(
t)/2
, λ0 = 0
, λ+ = Ω(
t)/2, respectively. Here
, and tan
θ(
t) = Ω
p(
t)/Ω
s(
t). The intermediate state |0〉 is called the dark state, which connects the |1〉 and |3〉 states without need of state |2〉. Maintaining the alignment of the state vector with the dark state (i.e., adiabatic following) is a basic feature of the STIRAP process. This requires that the adiabatic condition must be satisfied in the standard STIRAP [
41,
66].
Figure 1(b) shows the cdSTIRAP protocol. The only difference from STIRAP protocol is that an additional driving field CD is applied to compensate for the nonadiabatic excitation. Thus, the complete interaction Hamiltonian becomes
with
Here Ωcd(t) is the amplitude of the CD field and the phase ϕ = π/2.
For the purpose to obtain exact magnitude of Ω
cd(
t) and maintain the adiabatic evolution of the system, we convert the Hamiltonian
H2 into a new matrix with three eigenstates in (2) as the base vector. The transformation matrix [
52] is
Then, we make use of to represent the new matrix, which satisfies
Apparently,
Note that when we take
the off-diagonal elements in
will vanish [
52,
54,
67]. It means that the system will be locked in the dark state during adiabatic evolution, i.e., the three-level quantum battery can be charged or discharge through STA.
Consistent with Refs. [
39,
40], we define the battery energy at time
t is
E(
t) =
T r{
H0ρ(
t)}, where
ρ(
t) is the density matrix.
During charging, the ergotropy in quantum battery is
The charging power defines
while the discharging ergotropy is
and the discharging power is
where tc and td are the charging and discharging time, respectively.
3 Charging dynamics
We now study the charging characteristics of quantum battery via cdSTIRAP protocol. In following analyses, we consider the driving fields are Gaussian pulses, of the form
with delay τ , peak value Ω0 and width T . The additional driving field CD is realized by modulating
In all following calculations, for simplicity, we choose the energy spectrum of the three-level system as ε1 = 0, ε2 = 1 and ε3 = 1.95. The stable charging strategy for our quantum battery is through the eigenstate |0〉. Therefore the ergotropy is then
We assume that the system is initially prepared in the ground state (corresponding to a discharged battery). Figure 2 shows the variation characteristics of ergotropy, population of the second excited state and power over time under specific parameters. The red solid line indicates the adiabatic evolution in cdSTIRAP charging protocol. The blue triangles represent the analytical solution of Eq. (15). We find that the numerical results are in complete agreement with the analytical results of Eq. (15) for cdSTIRAP charging protocol. For comparison purposes, the STIRAP charging protocol is also depicted with a black dashed line under the same parameters. As shown in Fig. 2(a), due to the accelerating the evolution, the cdSTIRAP charging protocol realize the complete and stable charging of the quantum battery in a very short time. This can also be further demonstrated by the time evolution of the population. In Fig. 2(a), we show the time evolution of populations in the second excited state, which are represented by green solid circle and olive hollow circle for cdSTIRAP and STIRAP, respectively. The population can transfer quickly for cdSTIRAP, while it barely changes for STIRAP (only arrive to 3.75 × 10−3) at the end time. During the entire charging process, the ergotropy stored through STIRAP charging protocol is less than half of the maximum stored ergotropy. What’s more, it is interesting to find that the cdSTIRAP can significantly improve the charging power of the quantum battery in Fig. 2(b). At the initial moment, the difference between the charging power of the two cases can be neglected. With the increase of time, the advantage of counterdiabatic driving gradually appears. The charging power gradually reaches its maximum value at some point of time. Then, the two charging powers slowly drop as time goes on. During which the charging power of cdSTIRAP charging protocol always greater than the STIRAP one. It is worth attentioning that the maximum charging power increased more than four times. In the insets of Fig. 2, we display the charging process in the standard STIRAP protocol. Obviously, to achieve the adiabatic evolution of the quantum state and make the quantum battery fully charged, one has to increase the charging time to satisfy the adiabatic condition. As a result, the charging power is greatly reduced, the maximum value only 1% of the cdSTIRAP protocol.
The effect of delay τ and peak value Ω0 on maximum ergotropy and charging power is shown in Fig. 3. Figures 3(a) and (c) illustrate the dependencies of the maximum ergotropy and maximum charging power on delay time τ . It is noteworthy that the two charging protocols are identical when the value of τ is taken as 0 (corresponding to Ωcd = 0). Once the delay τ sets in, the two protocols immediately deviate from each other; the maximum ergotropy and charging power in the cdSTIRAP increase and the maximum ergotropy can approach and hold in the maximum value as τ increases [see also Eq. (15)], whereas those in the STIRAP decrease. Figures 3(b) and (d) show the maximum ergotropy and charging power as functions of Ω0. The cdSTIRAP charging protocol shows good stability; for different Ω0 it can always make the quantum battery fully charged. Interestingly, the maximum charging power is not influenced by Ω0. This is due to the fact that the charging ergotropy is independent to the peak value Ω0 [see Eq. (15)] and Ω0 = 0 corresponds to the case of the resonant π pulse (see also Appendix). The advantages of the cdSTIRAP protocol are quite obvious. Especially when the Ω0 is relatively small, the maximum ergotropy and charging power far exceed the STIRAP charging protocol.
4 Discharging character
The discharging process of the quantum battery can also be realized through STA. We assume that a quantum battery is already fully charged, i.e., the three-level system is on the second excited state, and the energy is extracted by transitioning it back to the ground state. Similarly, the STA is able to accelerate this discharging process.
In STIRAP discharging protocol, energy is released by changing the sequence of pulses. More specifically, the STIRAP discharging protocol exploits a first P pulse on |1〉–|2〉 transition and a second S pulse on |2〉–|3〉 transition. That means they take the form
As for cdSTIRAP discharging protocol, to ensure the quantum battery discharge through STA, a counterdiabatic pulse is added on this basis, which satisfies
Similarity, the corresponding discharging ergotropy is
Figure 4 presents the time evolution of ergotropy, population of the second excited state and power in two different discharging protocols. The blue triangles represent the analytical solution of Eq. (18). Clearly, the numerical results are in complete agreement with the analytical results of Eq. (18) for cdSTIRAP protocol. The STIRAP discharge protocol at most can only extract part of the energy stored in the quantum battery. In contrast, the cdSTIRAP discharge protocol can not only make full use of all the energy in the quantum battery, but also obviously release the energy faster [Fig. 4(a)]. This power advantage is also illustrated in Fig. 4(b), which is more suitable for some high-power appliances.
5 Implement
The cdSTIRAP charging and discharging protocols described here can be implemented in different physical systems driven by optical excitations or microwave excitations, like superconducting circuit and N–V centre. Supposing we use circuit quantum electrodynamics as the experimental platform [
54,
68], the first three states of a superconducting transmon circuit constitute a three-level quantum battery. Two microwave pulses are used to realize STIRAP, and an additional two-photon microwave pulse is needed to suppress nonadiabatic excitations and thereby realize cdSTIRAP. Encouragingly, just recently, an experimental realization of a three-level quantum battery based on superconducting qubits has been reported and the stable and powerful charging processes by exploring dark and bright states have also been achieved, respectively [
69]. The negatively charged N–V centre in the diamond lattice is also an excellent experimental platform [
55,
56]. It has a
S = 1 spin system which is equivalent to a three-level quantum battery in its orbital ground state. The N–V’s spin sublevels are |0〉 and | ± 1〉. It can achieve STIRAP charging or discharging protocol by driving the |0〉↔| ± 1〉 transitions with microwave magnetic fields. In addition, applying a time-varying strain field to control the |−1〉↔|+1〉 transition, which compensate for nonadiabatic transitions and implement the cdSTIRAP.
6 Conclusion and discussion
In conclusion, we have introduced the concept of a cd-STIRAP quantum battery, a three-level quantum system charged or discharged through STIRAP and STA based on counterdiabatic driving to accelerate charging or discharging processes. By calculation of the ergotropy and power variation over time, we have confirmed the significant acceleration effect of STA on the charging and discharging process of quantum battery. The maximum charge energy can be increased approximately 3 to 4 times, while the maximum charge power can be increased 4 to 5 times. In addition, we have also studied the impact of different delay τ and peak value Ω0 on the quantum battery. We found that the performance of a cdSTIRAP quantum battery not vary with peak value, but raising the value of delay time would lead to a larger maximum charging power. We finally proposed that superconducting circuit or N–V centre provide a promising implementation for our cdSTIRAP quantum batteries. This study aims to provide a more efficient three-level quantum battery theoretical background in view of future experimental implementations.
It is should be pointed out that (i) the present cd-STIRAP quantum batteries must employ a specific time-dependent additional field pulse Ω
cd; (ii) the additional field formes a closed interaction loop, which makes population transfer sensitive to the phases of the fields [
41]. These constraints render that the procedure would be impractical. One natural question is: If it is possible to perform a resonant π laser pulse in the |1〉–|3〉 transition, then this pulse will produce the desired population transfer without the need of the S and P pulses [
41]. In fact, if one is able to directly couple |1〉 to |3〉, the π pulse alone can transfer the population from |1〉 to |3〉 regardless of the pulse shape, i.e., no matter what kind of π pulse, the maximin energy of quantum battery can be reached. However, the battery power varies with the π pulse shape (see Appendix A). On the one hand, the π pulse is sensitive to pulse duration and peak amplitude. In addition, the use of the present cdSTIRAP scheme (which depends on at least two coherent pulses), rather than a single pulse coupling two states, offers many advantages: i) The transition efficiency can be made relatively insensitive to many of the experimental details of the pulses; ii) With the three-state system, one can produce transition between states for which the single-photon transitions are forbidden. Especially, it can be used to transfer population between magnetic sublevels or fine-structure levels [
42]; iii) It is much more efficient due to accelerating the adiabatic transition precess by using the third additional field pulse. Furthermore, in our quantum battery model, the detuning and the middle-state decay are not considered. When these factors are taken into account, high efficient quantum battery can still be achieved via non-Hermitian STA, but with a more complex additional fields form [
70]. After finishing this work, we became aware of a recent article [
71], in which a similar STA method is employed to speed up the adiabatic charging process of quantum batteries. The main qualitative features of our results agree with those in Ref. [
71] confirms the excellent performance of cdSTIRAP quantum batteries.