/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Q5P Show that if 蠄n is real, the ge... [FREE SOLUTION] | 91影视

91影视

Show that if n is real, the geometric phase vanishes. (Problems 10.3 and 10.4 are examples of this.) You might try to beat the rap by tacking an unnecessary (but perfectly legal) phase factor onto the eigenfunctions: n(t)e颈蠁苍n(t), wheren(R) is an arbitrary (real) function. Try it. You'll get a nonzero geometric phase, all right, but note what happens when you put it back into Equation 10.23. And for a closed loop it gives zero. Moral: For nonzero Berry's phase, you need (i) more than one time-dependent parameter in the Hamiltonian, and (ii) a Hamiltonian that yields nontrivially complex eigenfunctions.

Short Answer

Expert verified

The geometric phase is '(t)=e颈胃(t)e颈蠒(0)(t).There is no time dependent geometric phase.

Step by step solution

01

Define Dynamic phase.

Geometric phase is a phase difference gained during the course of a cycle when a system is subjected to cyclic adiabatic processes, which derives from the geometrical features of the Hamiltonian's parameter space in both classical and quantum mechanics.

02

Obtain the wave function.

Let the wave function after a time be,

n(t)0-1h0tEn(t')dt'...(2)

The equation is given by, localid="1656051708104" Yn(t)=i0t(t')l饾湑饾湑t'n(t')dt'......(3)

By using the normalization condition, n|n=1So, by differentiating to get:

ddtn|n=0=n|n+n|n=n|n'+n|n=2R(n|n)Thetermn(t')l饾湑饾湑t'n(t')mustbepurelyimaginaryandzeroifisreal.Consequently,isreal.

03

Obtain the new wave function.

Multiply the real function by the phase factor to get the new wave function: '=e颈蠒

It鈥檚 time derivative is '=颈蠒e颈蠒+e颈蠒. Thus,

'|'=|i+=i|i++=i+=0

The geometric phase for the modified function is,

Y'=i0ti蠒诲迟'n=-((t)-(0))

Substitute the value in the equation (1).

'(t)=eie(t)e-i((t)-(0))'(t)=eie(t)e-i((t)-(0))eie(t)(t)=eie(t)eie(0)(t)

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

(a) Derive the equation 10.67 from Equation 10.65.

(b) Derive Equation 10.79, starting with Equation 10.78.

(a) Use Equation 10.42 to calculate the geometric phase change when the infinite square well expands adiabatically from width w1to width w2. Comment on this result.

(b) If the expansion occurs at a constant rate(dw/dt=v), what is the dynamic phase change for this process?

(c) If the well now contracts back to its original size, what is Berry's phase for the cycle?

A particle starts out in the ground state of the infinite square well (on the interval 0 鈮 x 鈮 a) .Now a wall is slowly erected, slightly off center:

V(x)=f(t)(x-a2-)

wheref(t)rises gradually from 0toAccording to the adiabatic theorem, the particle will remain in the ground state of the evolving Hamiltonian.

(a)Find (and sketch) the ground state att Hint: This should be the ground state of the infinite square well with an impenetrable barrier ata/2+ . Note that the particle is confined to the (slightly) larger left 鈥渉alf鈥 of the well.

(b) Find the (transcendental) equation for the ground state energy at time t.
Answer:

zsinz=T[cosz-cos(z)]zsinz,wherezka,Tmaf(t)/h2,2/a,andk2mE/h. zsinz=T[cosz-cos(z)]zsinz,wherezka,Tmaf(t)/h2,2/a,andk=2mE/h

(c) Setting 未 = 0 , solve graphically for z, and show that the smallest z goes from 蟺 to 2蟺 as T goes from 0 to 鈭. Explain this result.

(d) Now set 未 = 0.01 and solve numerically for z, using

T=0,1,5,20,100,and1000

(e) Find the probability Prthat the particle is in the right 鈥渉alf鈥 of the well, as a function of z and 未. Answer:

Pr=1/[1+I+II-]Pr=1/[1+I+II?],whereI+[1-(z1)sin2[z1/2]

. Evaluate this expression numerically for the T鈥檚 and 未 in part (d). Comment on your results.

(f) Plot the ground state wave function for those same values of T and 未.
Note how it gets squeezed into the left half of the well, as the barrier grows.

The driven harmonic oscillator. Suppose the one-dimensional harmonic oscillator (mass m, frequency 蝇) is subjected to a driving force of the form F(t) = m 蝇虏 f(t) , where f(t) is some specified function. (I have factored out m 蝇虏 for notational convenience; f(t) has the dimensions of length.) The Hamiltonian is

H(t)=-h22m2x2+12m2x2-m2xf(t) (10.90).

Assume that the force was first turned on at time t=0:f(t)=0fort0t=0.This system can be solved exactly, both in classical mechanics and in quantum mechanics.

(a)Determine the classical position of the oscillator, assuming it started from rest at the origin (xc0=xc0=0). Answer:

xc(t)=0tf(t')sin[t-t']dt'.(10.91).

(b) Show that the solution to the (time-dependent) Schr枚dinger equation for this oscillator, assuming it started out in the nth state of the undriven oscillator (x,0=nx)wheren(x)is given by Equation 2.61), can be written as

n(x)=An(a^+)n0(x),withEn=(n+12)h (2.61).

localid="1656143246748" (x,1)=n(x-xc)eih[-(n+12)ht+mxc(x-xc2)+m220tf(t')xx(t')dt'](10.92).

(c) Show that the Eigen functions and Eigenvalues of H(t) are

n(x,t)=n(x-f);En(t)=(n+12)h-12m2f2 (10.93).

(d) Show that in the adiabatic approximation the classical position (Equation 10.91) reduces to xc(t)f(t)State the precise criterion for adiabaticity, in this context, as a constraint on the time derivative of f. Hint: Write sin[t-t']as(1/dt')cos[t-t']and use integration by parts.

(e) Confirm the adiabatic theorem for this example, by using the results in (c) and (d) to show that

(x,t)n(x,t)ein(t)ein(t)(10.94).

Check that the dynamic phase has the correct form (Equation 9.92). Is the geometric phase what you would expect?

ein(t),wheren(t)1hhtEn(t')dt'(9.92).

The delta function well (Equation 2.114) supports a single bound state (Equation 2.129). Calculate the geometric phase change whengradually increases from1to2. If the increase occurs at a constant rate, (诲伪/dt=c)what is the dynamic phase change for this process?

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.