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ORIGINAL RESEARCH article

Front. Phys., 13 January 2023
Sec. Atomic and Molecular Physics
This article is part of the Research Topic Quantum and Semiclassical Trajectories: Development and Applications View all 11 articles

Simulation of quantum shortcuts to adiabaticity by classical oscillators

Yang LiuYang Liu1Y. N. Zhang,Y. N. Zhang1,2H. D. Liu
H. D. Liu1*H. Y. Sun
H. Y. Sun1*
  • 1Center for Quantum Sciences and School of Physics, Northeast Normal University, Changchun, China
  • 2School of Science, Shenyang University of Technology, Shenyang, China

It is known that the dynamics and geometric phase of a quantum system can be simulated by classical coupled oscillators using the quantum−classical mapping method without loss of physics. In this work, we show that this method can also be used to simulate the schemes of quantum shortcuts to adiabaticity, which can quickly achieve the adiabatic effect through a non-adiabatic process. By mapping quantum systems by classical oscillators, two schemes, Berry’s “transitionless quantum driving” and the Lewis−Riesenfeld invariant method, are simulated by a corresponding transitionless classical driving method, which keeps adiabatic phase trajectories and acquires Hannay’s angle and the classical Lewis−Riesenfeld invariant method by manipulating the configurations of classical coupled oscillators. The classical shortcuts to adiabaticity for the two coupled classical oscillators, which is the classical version of a spin-1/2 in a magnetic field, is employed to illustrate our results and compared with quantum shortcuts-to-adiabaticity methods.

1 Introduction

Adiabatic processes of quantum systems have become a significant ingredient in quantum information processing for various practical purposes in metrology, interferometry, quantum computing, and control of chemical interaction [14]. Achieving state preparation or transferring the population with high fidelity versus parameter fluctuations should take a long time [57]. However, there are many instances where we need to speed these operations up to prevent them from suffering decoherence, noise, or losses [8, 9]. Therefore, proposing a way to speed up the adiabatic approaches has drawn considerable attention [1013]. So far, a variety of techniques to implement shortcuts to adiabaticity (STA) have been proposed [5, 8, 1421]. Notably, there is a shortcut passage algorithm proposed by Berry called “transitionless quantum driving” (TQD) [10]. This method accelerates adiabatic evolution in a hurry by designing a time-dependent interaction followed by the system exactly [10]. Moreover, Chen et al. put forward another method to accelerate the adiabatic passage using the Lewis−Riesenfeld (LR) invariant to keep the eigenstates of a Hamiltonian from a specified initial to the final configuration in an arbitrary time [8].

Not only STA techniques are developed in quantum systems but there are also dissipationless classical drivings in classical systems [20, 2226]. Moreover, it is already known that a quantum system in a Hilbert space possesses a mathematically canonical classical Hamiltonian structure in the phase space [2741]. For example, the structures of their phase spaces are usually regarded as the same [42, 43]. Classical and quantum mechanics can also be embedded in a unified formulation as a quantum−classical hybrid system [44]. There is a way to devote elements of quantum mechanics to classical mechanics, in which we can simulate the microscopic quantum behavior by a transition of the average value from a quantum system Hamiltonian into a classical system consisting of oscillators without losing any physics [4555]. Therefore, it is possible to map and generalize adiabatic processes and STA for quantum systems to classical systems by the quantum−classical mapping method. As a matter of fact, we are inspired to ask if we can simulate the STA in quantum systems by classical oscillators. Based on this mapping and simulation, can it give specific classical schemes for quantum schemes for the STA as the dissipationless classical driving did? What is the relation between the quantum and classical STA?

In this paper, we first introduce the quantum−classical mapping and the relation between the Berry phase for the original quantum system and Hannay’s angle for the mapped classical system in Section 2. In Section 3, we generalize and simulate the two kinds of STA methods, TQD and LR invariant-based methods, for quantum systems into the classical system through the quantum−classical mapping and construct a complete theoretical framework for both methods of achieving the STA in classical systems. On one hand, the TQD method which implements the STA by finding an additional Hamiltonian to drive the system can be simulated by adding an additional driving Hamiltonian to keep adiabatic phase trajectories and acquire Hannay’s angle [23, 24]. On the other hand, the LR invariant method which keeps energy eigenstates from a specified initial to the final configuration can also be simulated by manipulating the configurations of classical coupled oscillators [20, 22]. To illustrate these two classical methods, we study the quantum−classical mapping and the two STA methods for a spin-1/2 in a magnetic field, which corresponds to two coupled classical oscillators in Section 4. Finally, we give a conclusion in Section 5.

2 Adiabatic evolution in quantum−classical mapping

We consider an N-level quantum system governed by Hamiltonian Ĥ(t); its dynamical evolution can be described by the following Schrödinger equation (see Appendix for details):

idψntdt=HCψn*,(1)

with the probability amplitudes ψn of the state |Ψ⟩ = nψn(t)|ψn⟩ on the bare basis {|ψn⟩} and the mean value energy HC(ψ,ψ*,t)=Ψ|Ĥ(t)|Ψ, where ψ(t)=(ψ1(t),,ψn(t),,ψN(t))T. To study the adiabatic evolution of the system, it is convenient to transform the bare basis {|ψn⟩} into the adiabatic basis {|Ek(t)⟩}, which consists of the time-dependent eigenstates |Ek(t)⟩ of the Hamiltonian Ĥ(t). The amplitudes φ(t)=[φ1(t),,φn(t),,φN(t)]T on the adiabatic basis are determined by |Ψ⟩ = kφk(t)|Ek(t)⟩. These two bases can be connected by the unitary transformation given as follows:

ψt=Utφt,(2)

with Unk = ⟨ψn|Ek(t)⟩. By the adiabatic theorem, the probability |φk(t)|2 remains unchanged in the adiabatic limit. The phase of the amplitudes φk accumulated via evolution includes a dynamic phase ∫Ek(t)dt and a Berry phase γk = Ek(t)|dtEk(t)⟩dt [56].

This quantum adiabatic evolution can be equivalently mapped into a classical one without losing any physics [45, 46, 52]. If we decompose ψn into real and imaginary parts ψn(t)=[qn(t)+ipn(t)]/2, the Schrödinger equation and its complex conjugate can be written as Hamilton canonical Eqs 46, 47, 53, shown as follows:

q̇n=HCpn,ṗn=HCqn.(3)

The Hamiltonian HC(ψ, ψ*, t) can be transformed into h(q, p, t), and the quantum dynamics in Eq. 1 can be represented by the classical evolution of the “position variable q(t)” and “momentum variable p(t)” in Eq. 3.

The adiabatic evolution of adiabatic states can also be mapped to a classical one. One can introduce a new pair of variables (θ, I) corresponding to the amplitudes on the adiabatic basis by

φkt=Ikeiθkt(4)

and the Hamiltonian changes into [52]

HCθ,I,t=kEktIk/+Sq,I,tt,(5)

where Ek(t) corresponds to the eigenvalues of the Hamiltonian Ĥ, with corresponding eigenstates |Ek(t)⟩. S(q, I, t) is the generating function of the classical transformation (q(t), p(t)) → (θ(t), I)

pnt=k2IkcosθkImUnktsinθkReUnkt,qnt=k2IkcosθkReUnkt+sinθkImUnkt(6)

between the position−momentum variable and action−angle variable, which corresponds to the quantum unitary transformation |Ek(t)⟩ = nUnk(t)|ψn⟩ between the adiabatic basis and the bare basis. Under the adiabatic evolution, it has been proved that the two new variables θ(t) and I satisfy the same canonical equations as the angle−action variables in classical mechanics [46], given as follows:

θ̇k=Ekt/AHI;tIk,İk=0.(7)

Like the Berry phase, the adiabatic evolution will accumulate a dynamic angle ∫Ek(t)/ℏdt and an additional angle onto the angle variable called Hannay’s angle [57].

ΔθkI=IkAHI;t,(8)

where

AHI;t=pθ,I;ttqθ,I;tθ=12πNdθnpnθ,I;ttqnθ,I;t(9)

is the angle connection for Hannay’s angle [51]. The angular brackets ⟨⋯ ⟩θ denote the averaging over all angles θ (this averaging process is called the averaging principle, which can be treated as the classical adiabatic approximation), and t is defined as tF(t)=F(t)t. It can be proved that AH = kiIkAB(k; t) [52]. We note that AB(k; t) is nothing but a one-form for the Berry phase [51], and this means that Hannay’s angle is exactly equal to the minus Berry phase of the original quantum system [48, 52], which is given as follows:

ΔθkI=IkAHI;t=iABk;t=γk.(10)

So far, a quantum adiabatic evolution and its Berry phase can be perfectly mapped to a classical one and its Hannay’s angle. Next, we will show that the two different methods for the quantum STA can also be mapped to classical systems. It will not only connect the current methods for the classical STA to the quantum ones but also shed more light on the classical methods.

3 Shortcut to adiabaticity: From a quantum to classical system

3.1 Transitionless classical driving

We first discuss the transitionless tracking algorithm. For the non-adiabatic quantum driving, the quantum evolution cannot be restricted to an eigenstate, whatever the initial state is. According to the STA proposed by Berry, for the Hamiltonian Ĥ(t) we discussed in the previous section, if we want to keep no transitions between the eigenstates

|φnt=eiβn+γn|Ent(11)

of Ĥ(t) in the exact quantum evolution without the adiabatic approximation with the dynamic phase βn=10tEn(τ)dτ and the geometric phase γn=i0tEn(τ)|τEn(τ)dτ, we need an effective TQD Hamiltonian [10], given as follows:

Ĥeff=n|EntEntEnt|+in|tEntEnt|Ent|tEnt|EntEnt|.(12)

To drive state Eq. 11, the first sum in Eq. 12 is exactly the original Hamiltonian Ĥ(t) represented by the adiabatic basis, and the second sum contains two terms that cancel the transition between eigenstates and generate the accumulated Berry phase, respectively.

Similarly, for non-adiabatic classical driving, the evolution of the canonical coordinates q and p will also fail to keep the action variable I unchanged without the averaging principle, and their trajectories in the phase space will not follow adiabatic trajectories (see Figure 1B). Accordingly, the action variable I will be conserved in a classical evolution as long as the additional effects caused by the time-dependent canonical transformation are canceled. This means that if we want the Hamiltonian function driving the canonical variables as Eq. 7 without the average principle, the transitionless classical driving (TCD, no transition between action variables) Hamiltonian function can be written as follows [25]:

HCeffI;t=HCI;θ;t+HCII;θ;t=HCI;θ;tFtAH.(13)

FIGURE 1
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FIGURE 1. (A) Initial phase trajectory (solid line) and initial phase points (blue dots). (B) Final adiabatic trajectory (solid line) and final phase points driven by HC when t/τ = 1, τ = .5 (red dot blanks) and τ = 30 (blue dots). (C) Final adiabatic trajectory (solid line) and final phase points driven by HC + HCI, when t/τ = 1 and τ = .5 (blue dots). (D) Final adiabatic trajectory (solid line) and final phase points driven by HC + HCI, when t/τ = 2 and τ = .5 (blue dots). (E) Final adiabatic trajectory (solid line) and final phase points driven by HIeff, when t/τ = 1 and τ = .5 (blue dots). (F) Final adiabatic trajectory (solid line) and final phase points driven by HIeff, when t/τ = 2 and τ = .5 (blue dots).

With the quantum−classical mapping method we introduced in the last section, we can derive a more explicit form of the TCD Hamiltonian HCeff by averaging TQD Hamiltonian Ĥeff Eq. 12. After a straightforward derivation, we have

HCeff=ψ|Ĥeff|ψ=nEn|φn|2+in,mnφm*φnEm|tEn=nInωnnpnθ,I;ttqnθ,I;tθ+12npnθ,I;ttqnθ,I;tqnθ,I;ttpnθ,I;t=nInωnntpnθ,I;tqnθ,I;t,(14)

where ωn = En/ and the angular brackets ⟨⋯ ⟩ denote the averaging over all angle variables 1(2π)NΠkN02πdθk. Comparing Eq. 13 with Eq. 9, the terms canceling the non-adiabatic evolution and generating Hannay’s angle can be written as follows:

Ft=12nqnθ,I;ttpnθ,I;tpnθ,I;ttqnθ,I;t,AH=npnθ,I;ttqnθ,I;tθ,(15)

respectively. Like the TQD, the choice of eigenfrequencies ωn can be arbitrary and the geometric angles can be dropped for keeping the actions I conserved [10]. The simplest form of the Hamiltonian driving the canonical coordinates q and p with the conserved action I can be written as follows:

HIeff=12npnθ,I;ttqnθ,I;tqnθ,I;ttpnθ,I;t.(16)

3.2 LR invariant-based scheme

A different approach to realize the quantum STA is based on the LR invariants [8, 58]. For the Hamiltonian Ĥ(t), a time-dependent invariant can be determined by

iÎtt+Ît,Ĥt=0.(17)

The eigenvalues λn of Î(t) remain constant over time, and the time-dependent eigenstates |λn(t)⟩ will accumulate an LR phase

Ωnt=10tλnτ|iτHτ|λnτdτ(18)

via the dynamical evolution. By using the time-dependent unitary evolution operator

U=neiΩnt|λntλ0|,(19)

the Hamiltonian can be written as follows [8]:

ĤditUU=n|λntΩ̇nλnt|+in|tλntλnt|,(20)

where the second term can be used to drive the eigenstates |λn(t)⟩ of Î(t) and generate the LR phase. Without loss of generality, the arbitrariness of choosing Hd can be fixed by the constrain [Î(0),Ĥ(0)]=0 and [Î(t),Ĥ(t)]=0 [8]. Invariant condition Eq. 17 can also be derived by comparing Eq. 20 with the original form of Ĥ(t). Therefore, one can design an evolution path from the initial Hamiltonian Ĥ(0) to the final one Ĥ(T) along one of the eigenstates |λn(t)⟩ of Î(t) to achieve the STA.

For a classical system, we can also find similar classical time-dependent invariants that satisfy

J̇k=Jktt+Jkt,HCq,p;t=0.(21)

By introducing a new pair of variables including the time-dependent invariants (ξ, J) (hereafter referred to as LR variables), we have the following canonical equations:

J̇k=Gα,tξk=0,ξ̇k=Gα,tJk,(22)

where G(ξ, t) = HC(ξ, J, t) + S(ξ, J, t) is the Hamiltonian after a classical transformation (q(t), p(t)) → (ξ(t), J) with the generating function S(q, I, t). Since Jk are invariants, the Hamiltonian G(ξ, t) does not contain the angle variables ξk. The changes of angles then can be rewritten as follows:

Δξk=0TdtHCξ,J,tξIk+Sξ,J,tξIk,=0TdtH̄CJ,tIkALRJ,tIk(23)

with H̄C(J,t)HC(ξ,J,t)ξ and ALR(J,t)npn(ξ,J,t)tqn(ξ,J,t)ξ which is similar to the dynamical part and geometrical part in the angle changes of the classical adiabatic evolution. The angular brackets ⟨⋯ ⟩ξ denote an averaging over all LR angles ξ. Note that these LR variables are generally not action−angle variables of HC. However, we can set {Jk(0), HC(0)} = {Jk(T), HC(T)} = 0; the LR action variables Jk can, thus, be chosen as action variables that are related to the eigenfrequencies at initial time t = 0 and final time t = T. Similar to the quantum STA based on LR invariants, we can also design an evolution path from HC(0) to HC(T) with the invariants Jk, in which the initial action variables of H are equal to those in the final time.

To determine the specific form of the classical LR invariant-based scheme, we define the probabilities amplitudes dk of |Ψ⟩ = kdk|λk⟩ on the LR basis {|λk⟩} as

dk=Jkeiξk,(24)

using the quantum−classical mapping method. The canonical transformation (q, p) → (ξ, J) between position−momentum variables and LR variables can correspond to the quantum unitary transformation |λk(t)⟩ = nUnk(t)|ψn⟩ between the adiabatic basis and the bare basis given as follows:

pnt=k2JkcosξkImUnktsinξkReUnkt,qnt=k2JkcosξkReUnkt+sinξkImUnkt.(25)

Similar to the classical TQD scheme of the STA, the driving Hamiltonian should cancel the effect of the time-dependent transformation S and generate the angle Δξk. By Eqs 1323, we have

Hd=H̄CJ,tALRJ,tSt=HCξ,J,tξnpnξ,J,ttqnξ,J,tξ+12npnξ,J;ttqnξ,J;tqnξ,J;ttpnξ,J;t,(26)

with

St=12npnξ,J;ttqnξ,J;tqnξ,J;ttpnξ,J;t.(27)

According to the quantum−classical mapping, this classical Hamiltonian of LR invariants method is just the mean value of the quantum LR, given as follows:

Hd=ψ|Ĥd|ψ.(28)

Therefore, the form of LR variables can be determined by equating Hd and HC, and the boundary conditions are as follows:

Jk0,HC0=JkT,HCT=0.(29)

On the contrary, we can design the classical Hamiltonian Hd from the evolution of LR variables to realize the classical LR invariant-based scheme.

4 Spin-1/2 in a magnetic field

To illustrate our results, we consider the adiabatic evolution and STA scheme for a simple two-level quantum system, i.e., a spin-half particle with the magnetic moment μ in an external magnetic field B = B(sin α cos β, sin α sin β, cos α). Its Hamiltonian reads

Ĥ=μσ̂B=μBcosαsinαeiβsinαeiβcosα=μBcosα|++|||+sinαeiβ|+|+eiβ|+|,(30)

where σ̂=(σ̂1,σ̂2,σ̂3) are Pauli matrices and |±⟩ are the two spin eigenstates.

4.1 Transitionless classical driving

As we introduced in the previous section, if the two spin eigenstates |±⟩ are chosen as the basis, the Hamiltonian in Eq. 30 can be mapped to the classical Hamiltonian of a coupled oscillator, given as follows:

hp,q;B=μB12p22+q22p12q12cosα+p1q2p2q1sinαsinβ+q1q2+p1p2sinαcosβ,(31)

with |ψ⟩ = ψ1| − ⟩ + ψ2| + ⟩ and ψj=(qj+ipj)/2, (j = 1, 2). The canonical variables (q, p) satisfy the normalization condition [46], shown as follows:

j=12pj2+qj2=2.(32)

It is interesting to note that by defining a vector S = (S1, S2, S3) with

S1=σ1=q1q2+p1p2/,S2=σ2=p1q2p2q1/,S3=σ3=p22+q22p12q12/2,(33)

the Hamiltonian function can be written as follows:

hS;B=μSB,(34)

where the normalization condition of S is S2S12+S22+S32=1, and their Poisson bracket has a relation with the quantum commutator, shown as follows [45]:

Si,Sj=2εijkSk/=1iψ|σ̂i,σ̂j|ψ.(35)

We now move to calculate Hannay’s angle. Since the Hamiltonian in Eq. 30 has two eigenstates,

|E1=cosα2|++sinα2eiβ|,|E2=sinα2|++cosα2eiβ|,(36)

with eigenenergies −μB and μB, respectively. The canonical transformation (q, p) → (θ, I) and the mapped Hamiltonian function can be written as follows:

q1=2I1sinα2cosβθ1+2I2cosα2cosβθ2,q2=2I1cosα2cosθ12I2sinα2cosθ2,p1=2I1sinα2sinβθ1+2I2cosα2sinβθ2,p2=2I1cosα2sinθ1+2I2sinα2sinθ2,h̄I;B=μBI2I1/.(37)

We can calculate the forms of variable I by the following:

I1=21+Sb,I2=21Sb(38)

with q = (q1, q2), p = (p1, p2), θ = (θ1, θ2), I = (I1, I2), and b = B/B.

Therefore, we obtain the angle one-form by Eq. 9, given as follows:

AH=121cosαβ̇I1121+cosαβ̇I2.(39)

Hannay’s angles can, thus, be obtained by Eq. 10, given as follows:

Δθ1=121cosαβ̇dt,Δθ2=121+cosαβ̇dt,(40)

which differ from the Berry phases in the original quantum Hamiltonian [58] only by a sign.

By Eq. 14, we have the following:

HIeff=12p12q12β̇+p1q2p2q1cosβα̇p1p2+q1q2sinβα̇=2S31β̇+S2cosβα̇S1sinβα̇,(41)
AH=121cosαI1121+cosαI2=41cosα1+Sb+1+cosα1Sb=21cosαSb.(42)

Therefore, we can get the TCD Hamiltonian function

HCII;θ;X=2S31β̇+S2cosβα̇S1sinβα̇+21cosαSbβ̇=2B2SB×Bt,(43)

which takes a similar form as the counter-adiabatic driving Hamiltonian for spin-1/2 system Eq. 30. This means that the TCD scheme can be treated like a classical version of the TQD scheme by representing coordinate−momentum variables by the classical “spin” defined by Eq. 33.

We illustrate the evolution of the states through their trajectories in the phase space. The evolution of the points on phase trajectories can be determined by the dynamic equation of classical “spin,” given as follows:

Si̇=Si,HC=2μBεijkbjSkbkSj.(44)

By defining θ = arccos S2 and ϕ = arctan S2/S1, the dynamics of the original Hamiltonian HC takes the following form:

θ̇=2μBsinαsinβϕ,ϕ̇=2μBcosαsinαcosβϕtanθ.(45)

The parameters of the magnetic field B are chosen as

α=π2π4sinπtτ,β=ππ2cosπtτ,α̇=π24τcosπtτ,β̇=π22τsinπtτ,(46)

and μB/ = −1.

As shown in Figure 1B, the evolution of the canonical coordinates p and q will keep the action variable I almost unchanged, and their trajectories in the phase space will follow adiabatic trajectories when the frequency is slow.

For the TCD Hamiltonian HC + HCI, the effective magnetic field changes into the following:

Beff=B2μb×ḃ=Bsinαcosβ+2μBsinβα̇+sinαcosαcosββ̇i+sinαsinβ2μBcosβα̇sinαcosαsinββ̇j+cosα2μBsin2αβ̇k.(47)

The dynamics of the TCD Hamiltonian can, thus, be written as follows:

θ̇=cosβϕα̇sinαsinβϕ2μB+cosαβ̇,ϕ̇=2μBcosα+sin2αβ̇+sinαcosβϕ2μB/+cosαβ̇+sinβϕα̇tanθ.(48)

To drive the eigenstates using HC + HCI, the evolution of the canonical coordinates p and q will keep action variables I unchanged, and their trajectories in the phase space will follow adiabatic trajectories no matter how fast the frequency is (see Figures 1C, D). By tracing the same phase points of the initial phase trajectory (see Figure 1A) and the final adiabatic trajectory, we can find that there is an angle of shift after an adiabatic evolution. Also, the angle of shift after a whole period is double that after half a period.

Moreover, for the simplest Hamiltonian Eq. 41 [dropping the constant term and the term generating the Hannay’s angle Eq. 42], the dynamics of the simplest Hamiltonian HIeff is determined by the following:

θ̇=cosβϕα̇,ϕ̇=β̇+sinβϕα̇tanθ.(49)

It is easy to find that the adiabatic trajectories will remain unchanged after any period (see Figures 1E, F).

4.2 Classical LR invariant

In the approach of the LR invariant, the eigenstates of the LR invariant parallel to the eigenstates in Eq. 36 can be constructed as follows [8]:

|λ1=cosη2|++sinη2eiδ|,|λ2=sinη2|++cosη2eiδ|,(50)

and the LR invariant can be expressed as follows:

Ît=2Ω0cosηsinηeiδsinηeiδcosη.(51)

In the classical expression of the adiabatic process, without loss of generality, the time-dependent classical invariants can be designed by classical spin Eq. 33 as follows:

J1=21+Sb,J2=21Sb.(52)

where b′ = (sin η cos δ, sin η sin δ, cos η) is the scaling factor with the parameters (η, δ).

The canonical transformation between position−momentum variables (q, p) and LR variables (ξ, J) can be written as follows:

q1=2J1sinη2cosδξ1+2J2cosη2cosδξ2,q2=2J1cosη2cosξ12J2sinη2cosξ2,p1=2J1sinη2sinδξ1+2J2cosη2sinδξ2,p2=2J1cosη2sinξ1+2J2sinη2sinξ2.(53)

After this canonical transformation, the Hamiltonian h(q, p; B) becomes

GJ;B=H̄CJ;BALRJ;B=μBbJ2J1+12J11cosη+J21+cosηδ̇.(54)

We can calculate LR angles accumulated via the evolution process by Eq. 23, given as follows:

Δξ1=dtμBb121+cosηδ̇,Δξ2=dtμBb121cosηδ̇.(55)

According to Eq. 26, the driving Hamiltonian of the LR invariant-based scheme becomes

Hd=H̄CJ,tALRJ,tSt=μBbJ2J1+sinξ1ξ2η̇cosξ1ξ2sinηδ̇J1J2,=S3μBbcosη+2sin2ηδ̇+S1μBbsinηcosδ2sinδη̇+sinηcosηcosδδ̇+S2μBbsinηsinδ+2cosδη̇sinηcosηsinδδ̇=SBd,(56)

where Bd=(Bb)b2μb×ḃ. Comparing it with Eq. 34, the scaling factor b′ satisfies the following:

ḃ=2μb×B.(57)

The system invariant boundary conditions in Eq. 29 become

ḃ0=ḃT=0,(58)

and the driving magnetic field in the Hamiltonian H can be chosen as

B=2μb×ḃ(59)

to realize the evolution from initial energy eigenstates |λn(0)⟩ to final energy eigenstates |λn(T)⟩.

By equating Hamiltonian Hd Eq. 56 and H̄C(J,t), we can calculate these two pairs of parameters satisfying the following equation:

δ̇=2μBcosα+sinαcosηsinηcosβδ,η̇=2μBsinαsinβδ.(60)

In particular, there is still arbitrariness in the choice of parameters η and δ. To illustrate the adiabatic evolution driven by Eq. 56, we make the invariants of the initial and final moments satisfy the boundary conditions and Eq. 60. For example, to transfer the state from the first oscillator with canonical variables q1 and p1 to the second oscillator with canonical variables q2 and p2, we can set η̇(0)=0, η(0) = 0, and η(T) = π to satisfy the boundary conditions and chose a different scheme for δ.

To illustrate this result, we choose two different configurations of time-dependent parameters as shown in Figure 2. The first set of parameters

η=π2+π2cosπtτ,δ=π2+sinπtτ(61)

in Figure 2A which implements the adiabatic invariance of action variables can reproduce the evolution manipulated by the TQD Hamiltonian Eq. 43 as shown in Figure 2B. The action variables Ji exactly follow the adiabatic trajectories. The evolution of the phase trajectory is just like that in Figures 1A, E driven by HCeff. Similar to the fact that the TQD can be seen as one of the schemes for the inverse engineering based on the quantum LR invariant [59], the TCD which keeps the evolution exactly on the adiabatic trajectories in phase space of the classical Hamiltonian can be seen as one of the schemes for inverse engineering based on the classical LR invariant, which only needs the initial and final trajectories in the phase space matching adiabatic trajectories in the phase space of the classical Hamiltonian. Therefore, we can also design the classical Hamiltonian by different parameters to realize the classical LR invariant scheme. For example, the parameters

η=π3πt2+2πt3,δ=π2+π2t5π2t2+4πt32πt4(62)

in Figure 2C can also realize the state transfer between the two oscillators with a nearly unchanged δ. Thus, the optional form of the parameters to implement the adiabatic invariance is not unique. These results can be perfectly related to the LR invariant method for the spin-1/2 system [59].

FIGURE 2
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FIGURE 2. (A−C) Evolution of the parameters η (solid blue line) and δ (solid red line). (B−D) Time evolution of the action variables J1 (solid red line), J2 (solid blue line) driven by Hd, and adiabatic approximate invariants J1ad (dashed red line) and J2ad (dashed blue line) when t/τ = 1 and τ = .5.

5 Conclusion

To sum up, we use the quantum−classical mapping method to simulate the two schemes of the STA, i.e., the TQD and quantum LR invariant method, by the classical system consisting of coupled oscillators. On one hand, for the TQD, which implements the STA by finding an additional Hamiltonian to drive the system, we derived the explicit form of an additional driving Hamiltonian to keep the evolution of adiabatic phase trajectories and acquire the Hannay’s phase. This TCD method can perfectly simulate and match the TQD method. On the other hand, the Lewis−Riesenfeld invariant method, which keeps the energy eigenstates from a specified initial to the final configuration, can also be simulated by manipulating the configurations of classical coupled oscillators. Both of the approaches can accelerate the adiabatic process effectively under different circumstances and matches the quantum methods of the STA. These results prove that the protocol of the quantum−classical mapping can be used to generalize quantum schemes of the STA into the classical system. By this simulation, our theory could be expected to find applications of the STA for classical systems.

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding authors.

Author contributions

HL and HS initiated the idea. YL and HL wrote the main manuscript text. YL and YZ performed the calculations.

Funding

This work was supported by the National Natural Science Foundation of China (Contact Nos. 11875103 and 12147206).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

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Appendix: Derivation of the Schrödinger equation in the canonical form

The dynamical evolution of the N-level quantum system governed by the Hamiltonian Ĥ(t) can be described by the following Schrödinger equation:

it|Ψ=Ĥt|Ψ,(63)

which can be expanded by the quantum state |Ψ⟩ = ∑ψn(t)|ψn⟩ as follows:

itnψnt|ψn=Ĥt|Ψ,(64)

with the probability amplitudes ψn on the bare basis {|ψn⟩}. Since {|ψn⟩} is a time-independent bare basis, Eq. 64 becomes

idtψnt|ψn=Ĥt|Ψ.(65)

Multiplying Eq. 65 by ⟨ψm|, we have the following:

idtψmt=ψm|Ĥt|Ψ,(66)

with HC(ψ,ψ*,t)=Ψ|Ĥ(t)|Ψ=mψm*m|Ĥ(t)|Ψ. Therefore, the Schrödinger equation in the canonical form can be written as follows:

idψmtdt=HCψm*,(67)

which is just the same as Eq. 1.

Keywords: shortcut to adiabaticity, quantum−classical mapping, transitionless quantum driving, Lewis−Riesenfeld invariant, geometric phase

Citation: Liu Y, Zhang YN, Liu HD and Sun HY (2023) Simulation of quantum shortcuts to adiabaticity by classical oscillators. Front. Phys. 10:1090973. doi: 10.3389/fphy.2022.1090973

Received: 06 November 2022; Accepted: 28 December 2022;
Published: 13 January 2023.

Edited by:

Libin Fu, Graduate School of China Academy of Engineering Physics, China

Reviewed by:

Arkajit Mandal, Columbia University, United States
Yue Ban, Basque Research and Technology Alliance (BRTA), Spain

Copyright © 2023 Liu, Zhang, Liu and Sun. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: H. D. Liu, bGl1aGQxMDBAbmVudS5lZHUuY24=; H. Y. Sun, c3VuaHk1MDdAbmVudS5lZHUuY24=

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.