DOCSLIB.ORG

Physics 505 Homework No. 6 Solutions S6-1 1. Probability

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Physics 505 Homework No. 6 Solutions S6-1 1. Probability Physics 505 Homework No. 6 Solutions S6-1 1. Probability conservation (based on a problem in Schwabl). Recall that the Hamiltonian for a charged particle (charge e) of mass m in an electromagnetic field described by the potentials φ(x,t) and A(x,t) is, 1 e 2 H = p − A + eφ . 2m c Show that a wave function ψ which is a solution of Schroedinger’s equation with this Hamiltonian, satisfies the probability continuity condition, ∂ (ψ∗ψ) + ∇· j =0 , ∂t with j defined as ¯h 2ie j = ψ∗(∇ψ) − (∇ψ∗)ψ − Aψ∗ψ 2mi ¯hc 1 ¯h e ¯h e = ψ∗ ∇ − A ψ + ψ ∇ − A ψ∗ . 2m i c −i c Note that A is assumed to be real. Solution To start with, calculate −∇ · j using the j given above. −1 ¯h ¯h −∇ · j = (∇ψ∗) · (∇ψ) + (∇ψ) · (∇ψ∗) 2m i −i " e e + − A · (∇ψ∗) ψ − A · (∇ψ) ψ∗ c c ¯h ¯h + ψ∗∇2ψ + ψ∇2ψ∗ i −i e e + − ψ∗(∇· A)ψ − ψ(∇· A)ψ∗ c c e e + − ψ∗(A · ∇)ψ − ψ(A · ∇)ψ∗ . c c # Only the terms in the first line cancel! It’s tempting to get rid of the ∇· A terms, but we’re not necessarily in a static situation or the Coulomb gauge. Simplifying slightly, 1 ¯h −∇ · j = −ψ∗∇2ψ + ψ∇2ψ∗ 2m" i e +2 (ψ∗(A · ∇)ψ + ψ(A · ∇)ψ∗ + ψ∗ψ(∇· A)) . c # Copyright c 2012, Edward J. Groth Physics 505 Homework No. 6 Solutions S6-2 The Schroedinger equation is ∂ψ Hψ = i¯h . (1) ∂t For it’s complex conjugate, we might be tempted to write ∂ψ∗ Hψ∗ = −i¯h , ∂t but this only works when H = p2/2m + V . In this case, we need to be careful. ∗ 1 ¯h e 2 1 ¯h e 2 ∂ψ∗ (Hψ)∗ = ∇ − A + eφ ψ∗ = ∇ − A + eφ ψ∗ = −i¯h . 2m i c 2m −i c ∂t ! ! (2) Multiply the first equation by ψ∗, the second by ψ, and subtract. ∂ ∂ψ ∂ψ∗ (ψ∗ψ) = ψ∗ + ψ ∂t ∂t ∂t −i = (ψ∗Hψ − ψH∗ψ∗) ¯h −i 1 ¯h e 2 1 ¯h e 2 = ψ∗ ∇ − A ψ − ψ ∇ − A ψ∗ + ψ∗eφψ − ψeφψ∗ ¯h 2m i c 2m −i c ! 1 ¯h ¯h = − ψ∗∇2ψ + ψ∇2ψ∗ 2m i i " e e + ψ∗(∇· A)ψ + ψ(∇· A)ψ∗ c c e e + ψ∗(A · ∇ψ) + ψ(A · ∇ψ∗) c c e e + ψ∗(A · ∇ψ) + ψ(A · ∇ψ∗) c c ie2 ie2 + − ψ∗A2ψ + ψA2ψ∗ , ¯hc2 ¯hc2 # which simplifies slightly to ∂ 1 ¯h (ψ∗ψ) = −ψ∗∇2ψ + ψ∇2ψ∗ ∂t 2m" i e +2 (ψ∗(A · ∇)ψ + ψ(A · ∇)ψ∗ + ψ∗ψ(∇· A)) , c # which is the same as we previously obtained for −∇ · j. Copyright c 2012, Edward J. Groth Physics 505 Homework No. 6 Solutions S6-3 Some comments. p − eA/c = mv is the kinetic momentum operator. The extra terms with A in the current come about because we need to correct the canonical momentum to get the kinetic momentum. ψ∗ψ and j as defined above are the matter probability density and the matter proba- bility current. How would you write the charge probability density and charge probability current? (Answer: multiply them by e.) End Solution 2. Crossed E and B fields (based on a problem in Schwabl). Consider a particle with mass m and charge e moving in uniform B = Bez and E = Eex fields with E<B. Use the gauge A = Bxey. The Hamiltonian is 1 e 2 H = p − A − eEx . 2m c Find the eigenfunctions and eigenvalues for this Hamiltonian. Note that if you should find that the eigenfunctions involve standard functions which we already know about, you don’t have to write out each one explicitly. For example, if you should find (you won’t) that the eigenfunctions involve the Legendre polynomials Pl(y), you can just leave Pl(y) in your result rather than explicitly write out what Pl(y) is. Of course, you have to say that Pl stands for a Legendre polynomial of order l. Hint: you might start by reminding yourself what the classical motion looks like. Solution To start with the classical motion, there is no force in the z direction, so the z- component of velocity is constant. Note that if the particle has vy = −cE/B, then the magnetic force exactly cancels the electric force and the particle moves at constant velocity in the negative y direction. If the particle has vy different from above or a non-vanishing vx, then the motion is circular motion in the xy-plane (clockwise as viewed from the positive z-direction) with a velocity in the −y-direction at vy = −cE/B. (Often called E × B drift.) So, we are looking for eigenfunctions which have a constant vz (or pz) along with circular and linear motion in the xy-plane. Writing out the Hamiltonian, we have p2 1 e 2 1 H = x + p − Bx + p2 − eEx . 2m 2m y c 2m z We see that py and pz commute with the Hamiltonian, so our eigenfunctions can be eigenfunctions of py, pz, and H, simultaneously. Let pzψ =¯hkzψ and pyψ =¯hkyψ. Then the eigenvalue equation becomes 1 1 e 2 ¯h2k2 p2 + ¯hk − Bx − eEx ψ = E − z ψ = E′ψ, 2m x 2m y c 2m Copyright c 2012, Edward J. Groth Physics 505 Homework No. 6 Solutions S6-4 where we have used E to stand for the energy eigenvalue to distinguish it from E and E′ for the energy eigenvalue with the energy due to the z motion removed. Define ω = eB/mc and v0 = cE/B. Then the time independent Schroedinger equation becomes 1 1 p2 + (¯hk − mωx)2 − mωv x ψ = E′ψ, 2m x 2m y 0 Let’s work on the terms above involving x. 1 mω2 ¯hk v ¯h2k2 (¯hk − mωx)2 − mωv x = x2 − 2 y + 0 x + y . 2m y 0 2 mω ω m2ω2 ! Define ¯hk v x = y + 0 . 0 mω ω Then 2 2 2 1 2 mω 2 ¯h ky 2 (¯hky − mωx) − mωv0x = (x − x0) + 2 2 − x0 2m 2 m ω ! mω2 1 = (x − x )2 − mv2 − ¯hk v . 2 0 2 0 y 0 We can clean up the last two terms by adding and subtracting eEx0, 1 1 ¯hk v − mv2 − ¯hk v + eEx − eEx = − mv2 − ¯hk v + mωv y + 0 − eEx 2 0 y 0 0 0 2 0 y 0 0 mω ω 0 1 = mv2 − eEx . 2 0 0 Returning to the time independent Schroedinger equation, we have 1 mω2 1 ¯h2k2 p2 + (x − x )2 + mv2 − eEx ψ = E − z ψ, 2m x 2 0 2 0 0 2m So we see that the x motion is that of a harmonic oscillator centered at x0 with frequency ω. The energy eigenvalues are ¯h2k2 1 E =(n +1/2)¯hω + z + mv2 − eEx , n,ky ,kz 2m 2 0 0 withhk ¯ y = mωx0 − mv0 and (unnormalized) eigenfunction ikyy ikzz ψn,ky ,kz = ψn(x − x0)e e , where ψn is the harmonic oscillator eigenfunction with frequency ω and quantum number n. Copyright c 2012, Edward J. Groth Physics 505 Homework No. 6 Solutions S6-5 So, the motion has an energy corresponding to whatever kinetic energy we want in the z-direction, the kinetic energy due to the drift velocity in the y-direction and the kinetic energy due a harmonic oscillator at frequency ω in the x-direction. Since the center of oscillation is x0, there is also an electric potential energy −eEx0. Classically, the kinetic 2 2 energy due to the motion in the xy plane looks like mvx/2 + m(vy − v0) /2 where vx and vy are the velocity components of the circular motion relative to the center of the circle 2 2 2 which is moving with velocity −v0ey. Averaging over a period gives mr ω /2 + mv0/2 where r is the radius of the circular orbit. The cross term in the y-velocity averages to zero as does the variation in the electric potential energy as the particle oscillates in x. In the quantum case, the oscillator energy corresponds to mr2ω2/2. You might wonder where the drift velocity went in all this. Let ¯hΩ = En,ky ,kz , so Ω is the oscillation frequency of the wave function. Then the group velocity component in the y-direction is dΩ/dky. The only place ky appears in the energy is in x0. Carrying out the differentiation, we find vg = −cE/B = −v0, exactly the classical drift velocity. End Solution 3. Magnetic barrier. This problem appeared on the May, 2002 prelims. The Θ functions used below are defined so that Θ(x)=0if x < 0, Θ(x)=1if x > 0 and Θ(0) = 1/2. x ′ ′ In other words, Θ is the unit step function and Θ(x) = −∞ δ(x ) dx . Also you may find problem 1 in this assignment to be useful. R Consider a charged particle moving in the xy-plane subject to a magnetic field Bz = BΘ(x)Θ(d − x). The magnetic field is constant in a strip of width d and zero everywhere else. We will study the problem of scattering of plane waves from this “magnetic barrier.” (a) Write down the Schroedinger Hamiltonian for this problem. You have to choose a gauge for the vector potential—choose the gauge Ax = Az = 0, and also choose Ay = 0 for x < 0. Solution The vector potential is ∇ × A = B. We take Ay = 0 for x < 0, Ay = Bx for 0 ≤ x ≤ d and Ay = Bd for d<x.
Load more

Recommended publications
  • A Study of Fractional Schrödinger Equation-Composed Via Jumarie Fractional Derivative
    A Study of Fractional Schrödinger Equation-composed via Jumarie fractional derivative Joydip Banerjee1, Uttam Ghosh2a , Susmita Sarkar2b and Shantanu Das3 Uttar Buincha Kajal Hari Primary school, Fulia, Nadia, West Bengal, India email- [email protected] 2Department of Applied Mathematics, University of Calcutta, Kolkata, India; 2aemail : [email protected] 2b email : [email protected] 3 Reactor Control Division BARC Mumbai India email : [email protected] Abstract One of the motivations for using fractional calculus in physical systems is due to fact that many times, in the space and time variables we are dealing which exhibit coarse-grained phenomena, meaning that infinitesimal quantities cannot be placed arbitrarily to zero-rather they are non-zero with a minimum length. Especially when we are dealing in microscopic to mesoscopic level of systems. Meaning if we denote x the point in space andt as point in time; then the differentials dx (and dt ) cannot be taken to limit zero, rather it has spread. A way to take this into account is to use infinitesimal quantities as ()Δx α (and ()Δt α ) with 01<α <, which for very-very small Δx (and Δt ); that is trending towards zero, these ‘fractional’ differentials are greater that Δx (and Δt ). That is()Δx α >Δx . This way defining the differentials-or rather fractional differentials makes us to use fractional derivatives in the study of dynamic systems. In fractional calculus the fractional order trigonometric functions play important role. The Mittag-Leffler function which plays important role in the field of fractional calculus; and the fractional order trigonometric functions are defined using this Mittag-Leffler function.
    [Show full text]
  • L the Probability Current Or Flux
    Atomic and Molecular Quantum Theory Course Number: C561 L The Probability Current or flux 1. Consider the time-dependent Schr¨odinger Equation and its complex conjugate: 2 ∂ h¯ ∂2 ıh¯ ψ(x, t)= Hψ(x, t)= − 2 + V ψ(x, t) (L.26) ∂t " 2m ∂x # 2 2 ∂ ∗ ∗ h¯ ∂ ∗ −ıh¯ ψ (x, t)= Hψ (x, t)= − 2 + V ψ (x, t) (L.27) ∂t " 2m ∂x # 2. Multiply Eq. (L.26) by ψ∗(x, t), andEq. (L.27) by ψ(x, t): ∂ ψ∗(x, t)ıh¯ ψ(x, t) = ψ∗(x, t)Hψ(x, t) ∂t 2 2 ∗ h¯ ∂ = ψ (x, t) − 2 + V ψ(x, t) (L.28) " 2m ∂x # ∂ −ψ(x, t)ıh¯ ψ∗(x, t) = ψ(x, t)Hψ∗(x, t) ∂t 2 2 h¯ ∂ ∗ = ψ(x, t) − 2 + V ψ (x, t) (L.29) " 2m ∂x # 3. Subtract the two equations to obtain (see that the terms involving V cancels out) 2 2 ∂ ∗ h¯ ∗ ∂ ıh¯ [ψ(x, t)ψ (x, t)] = − ψ (x, t) 2 ψ(x, t) ∂t 2m " ∂x 2 ∂ ∗ − ψ(x, t) 2 ψ (x, t) (L.30) ∂x # or ∂ h¯ ∂ ∂ ∂ ρ(x, t)= − ψ∗(x, t) ψ(x, t) − ψ(x, t) ψ∗(x, t) (L.31) ∂t 2mı ∂x " ∂x ∂x # 4. If we make the variable substitution: h¯ ∂ ∂ J = ψ∗(x, t) ψ(x, t) − ψ(x, t) ψ∗(x, t) 2mı " ∂x ∂x # h¯ ∂ = I ψ∗(x, t) ψ(x, t) (L.32) m " ∂x # (where I [···] represents the imaginary part of the quantity in brackets) we obtain ∂ ∂ ρ(x, t)= − J (L.33) ∂t ∂x or in three-dimensions ∂ ρ(x, t)+ ∇·J =0 (L.34) ∂t Chemistry, Indiana University L-37 c 2003, Srinivasan S.
    [Show full text]
  • Relativistic Quantum Mechanics 1
    Relativistic Quantum Mechanics 1 The aim of this chapter is to introduce a relativistic formalism which can be used to describe particles and their interactions. The emphasis 1.1 SpecialRelativity 1 is given to those elements of the formalism which can be carried on 1.2 One-particle states 7 to Relativistic Quantum Fields (RQF), which underpins the theoretical 1.3 The Klein–Gordon equation 9 framework of high energy particle physics. We begin with a brief summary of special relativity, concentrating on 1.4 The Diracequation 14 4-vectors and spinors. One-particle states and their Lorentz transforma- 1.5 Gaugesymmetry 30 tions follow, leading to the Klein–Gordon and the Dirac equations for Chaptersummary 36 probability amplitudes; i.e. Relativistic Quantum Mechanics (RQM). Readers who want to get to RQM quickly, without studying its foun- dation in special relativity can skip the first sections and start reading from the section 1.3. Intrinsic problems of RQM are discussed and a region of applicability of RQM is defined. Free particle wave functions are constructed and particle interactions are described using their probability currents. A gauge symmetry is introduced to derive a particle interaction with a classical gauge field. 1.1 Special Relativity Einstein’s special relativity is a necessary and fundamental part of any Albert Einstein 1879 - 1955 formalism of particle physics. We begin with its brief summary. For a full account, refer to specialized books, for example (1) or (2). The- ory oriented students with good mathematical background might want to consult books on groups and their representations, for example (3), followed by introductory books on RQM/RQF, for example (4).
    [Show full text]
  • Photon Wave Mechanics: a De Broglie - Bohm Approach
    PHOTON WAVE MECHANICS: A DE BROGLIE - BOHM APPROACH S. ESPOSITO Dipartimento di Scienze Fisiche, Universit`adi Napoli “Federico II” and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli Mostra d’Oltremare Pad. 20, I-80125 Napoli Italy e-mail: [email protected] Abstract. We compare the de Broglie - Bohm theory for non-relativistic, scalar matter particles with the Majorana-R¨omer theory of electrodynamics, pointing out the impressive common pecu- liarities and the role of the spin in both theories. A novel insight into photon wave mechanics is envisaged. 1. Introduction Modern Quantum Mechanics was born with the observation of Heisenberg [1] that in atomic (and subatomic) systems there are directly observable quantities, such as emission frequencies, intensities and so on, as well as non directly observable quantities such as, for example, the position coordinates of an electron in an atom at a given time instant. The later fruitful developments of the quantum formalism was then devoted to connect observable quantities between them without the use of a model, differently to what happened in the framework of old quantum mechanics where specific geometrical and mechanical models were investigated to deduce the values of the observable quantities from a substantially non observable underlying structure. We now know that quantum phenomena are completely described by a complex- valued state function ψ satisfying the Schr¨odinger equation. The probabilistic in- terpretation of it was first suggested by Born [2] and, in the light of Heisenberg uncertainty principle, is a pillar of quantum mechanics itself. All the known experiments show that the probabilistic interpretation of the wave function is indeed the correct one (see any textbook on quantum mechanics, for 2 S.
    [Show full text]
  • Electron Spin and Probability Current Density in Quantum Mechanics W
    Electron spin and probability current density in quantum mechanics W. B. Hodgea) and S. V. Migirditch Department of Physics, Davidson College, Davidson, North Carolina 28035 W. C. Kerrb) Olin Physical Laboratory, Wake Forest University, Winston-Salem, North Carolina 27109 (Received 13 August 2013; accepted 26 February 2014) This paper analyzes how the existence of electron spin changes the equation for the probability current density in the quantum-mechanical continuity equation. A spinful electron moving in a potential energy field experiences the spin-orbit interaction, and that additional term in the time- dependent Schrodinger€ equation places an additional spin-dependent term in the probability current density. Further, making an analogy with classical magnetostatics hints that there may be an additional magnetization current contribution. This contribution seems not to be derivable from a non-relativistic time-dependent Schrodinger€ equation, but there is a procedure described in the quantum mechanics textbook by Landau and Lifschitz to obtain it. We utilize and extend their procedure to obtain this magnetization term, which also gives a second derivation of the spin-orbit term. We conclude with an evaluation of these terms for the ground state of the hydrogen atom with spin-orbit interaction. The magnetization contribution is generally the larger one, except very near an atomic nucleus. VC 2014 American Association of Physics Teachers. [http://dx.doi.org/10.1119/1.4868094] I. INTRODUCTION occurs early in the course (and the textbook) when only the simplest form of the time-dependent Schrodinger€ equation has The probability interpretation of the wave function w of a been introduced.
    [Show full text]
  • Probability Structure of Time Fractional Schrödinger Equation
    Vol. 116 (2009) ACTA PHYSICA POLONICA A No. 2 Probability Structure of Time Fractional Schrödinger Equation A. Tofighi¤ Department of Physics, Faculty of Basic Science, University of Mazandaran P.O. Box 47416-1467, Babolsar, Iran (Received July 19, 2007; in final form July 1, 2009) We consider the motion of a particle under the influence of a real potential within the framework of time fractional Schrödinger equation in 1 + 1 dimensions. For the basis states we obtain a simple expression for the probability current equation. In the limit where the order of fractional derivative is close to unity we find a fluctuating probability density for the basis states. We also provide a compact expression for the time rate of change of the probability density in this case. For the special case where the order of fractional derivative is equal 1 to 2 we compute the probability density. PACS numbers: 03.65.¡w 1. Introduction Utilizing a powerful expansion method [9, 10] we find the wave function and the probability density. We prove that Fractional quantum mechanics is a theory to discuss for the basis state the probability density increases ini- quantum phenomena in fractal environments. There has tially, then fluctuates around a constant value in later been many investigations on the subject. It is formulated times. We express the time rate of change of this prob- as a path integral over Lévy flight [1, 2], or from Nottale’s ability density in terms of simple function. We see that scale relativity theory [3, 4]. An algebraic treatment of in the steady state it fluctuates around zero.
    [Show full text]
  • Relativistic Quantum Mechanics
    Relativistic Quantum Mechanics Dipankar Chakrabarti Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India (Dated: August 6, 2020) 1 I. INTRODUCTION Till now we have dealt with non-relativistic quantum mechanics. A free particle satisfying ~p2 Schrodinger equation has the non-relatistic energy E = 2m . Non-relativistc QM is applicable for particles with velocity much smaller than the velocity of light(v << c). But for relativis- tic particles, i.e. particles with velocity comparable to the velocity of light(e.g., electrons in atomic orbits), we need to use relativistic QM. For relativistic QM, we need to formulate a wave equation which is consistent with relativistic transformations(Lorentz transformations) of special theory of relativity. A characteristic feature of relativistic wave equations is that the spin of the particle is built into the theory from the beginning and cannot be added afterwards. (Schrodinger equation does not have any spin information, we need to separately add spin wave function.) it makes a particular relativistic equation applicable to a particular kind of particle (with a specific spin) i.e, a relativistic equation which describes scalar particle(spin=0) cannot be applied for a fermion(spin=1/2) or vector particle(spin=1). Before discussion relativistic QM, let us briefly summarise some features of special theory of relativity here. Specification of an instant of time t and a point ~r = (x, y, z) of ordinary space defines a point in the space-time. We’ll use the notation xµ = (x0, x1, x2, x3) ⇒ xµ = (x0, xi), x0 = ct, µ = 0, 1, 2, 3 and i = 1, 2, 3 x ≡ xµ is called a 4-vector, whereas ~r ≡ xi is a 3-vector(for 4-vector we don’t put the vector sign(→) on top of x.
    [Show full text]
  • Bohmian Mechanics
    Bohmian Mechanics Roderich Tumulka Waterloo, March 2010 Roderich Tumulka Bohmian Mechanics Richard Feynman (1959): Does this mean that my observations become real only when I observe an observer observing something as it happens? This is a horrible viewpoint. Do you seriously entertain the thought that without observer there is no reality? Which observer? Any observer? Is a fly an observer? Is a star an observer? Was there no reality before 109 B.C. before life began? Or are you the observer? Then there is no reality to the world after you are dead? I know a number of otherwise respectable physicists who have bought life insurance. By what philosophy will the universe without man be understood? [R.P. Feynman, F.B. Morinigo, W.G. Wagner: Feynman Lectures on Gravitation (Addison-Wesley Publishing Company, 1959). Edited by Brian Hatfield] Roderich Tumulka Bohmian Mechanics Names of Bohmian mechanics pilot wave theory (de Broglie), ontological interpretation of quantum mechanics (Bohm), de Broglie-Bohm theory (Bell), ... Roderich Tumulka Bohmian Mechanics Definition of Bohmian mechanics (version suitable for N spinless particles in non-relativistic space-time) Electrons and other elementary particles have precise positions at every t 3 Qk (t) ∈ R position of particle k, Q(t) = (Q1(t),..., QN (t)) config., dQ (t) ∇ ψ k = ~ Im k t (Q(t)) (k = 1,..., N) dt mk ψt 3 N The wave function ψt :(R ) → C evolves according to N ∂ψ 2 X ~ 2 i~ = − ∇k ψ + V ψ ∂t 2mk k=1 Probability Distribution 2 ρ(Q(t) = q) = |ψt (q)| [Slater 1923, de Broglie 1926, Bohm 1952,
    [Show full text]
  • The De Broglie-Bohm Theory As a Rational Completion of Quantum Mechanics
    THE DE BROGLIE-BOHM THEORY AS A RATIONAL COMPLETION OF QUANTUM MECHANICS SCHOOL ON PARADOXES IN QUANTUM PHYSICS JOHN BELL INSTITUTE FOR THE FOUNDATIONS OF PHYSICS Hvar, Croatia 2 SEPTEMBER 2019 Jean BRICMONT Institut de Recherche en Math´ematique et Physique UCLouvain BELGIUM WHAT IS THE MEANING OF THE WAVE FUNCTION? IN ORTHODOX QUANTUM MECHANICS Ψ = STATE: VECTOR IN A HILBERT SPACE, 2 N e.g. L (R ). WHICH EVOLVES IN TIME: Ψ0 −! Ψt = U(t)Ψ0 U(t) UNITARY OPERATOR = SOLUTION OF SCHRODINGER'S¨ EQUA- TION A= AN \OBSERVABLE" = SELF-ADJOINT OPERATOR ACTING ON THAT HILBERT SPACE. IF A HAS A BASIS OF EIGENVEC- TORS: AΨi = λiΨi WRITE Ψ IN THAT BASIS P P 2 Ψ = i ciΨi with i jcij = 1. THEN, WE HAVE THE BORN RULE ABOUT PROBABILITIES OF RESULTS OF MEASURE- MENTS P(Result = λi when measure A, if state = Ψ) 2 = jcij AFTER THAT, THE STATE JUMPS OR IS REDUCED OR COLLAPSES TO Ψi. The meaning of Ψ comes only from measure- ments. As John Bell puts it: It would seem that the theory is exclu- sively concerned about \results of mea- surement", and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of \mea- surer"? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system::: with a Ph D? A DEEPER PROBLEM. Existential angst: Am I a vector Ψ in a Hilbert space? Which is, in part, simply a function defined on a high-dimensional space, such as 2 N Ψ 2 L (R )? What about you? That is why I don't agree with the notion that the quantum state even could be a \complete description" of a physical system.
    [Show full text]
  • Relativistic Quantum Mechanics
    Relativistic Quantum Mechanics Special relativity and quantum mechanics fit together nicely. We have already handled one relativistic particle, the photon. In this section, we learn how to treat other particles when their velocities are no longer negligible compared to the speed of light. Relativity Review Basically, we want to formulate quantum mechanics in a way that relativistic invariance is manifest. In classical physics, this is accomplished by the use of 4-vectors. To establish notation, we briefly review classical relativity in the language of 4-vectors. The coordinate 3-vector and time are the basic components of the 4-vector xµ; spec- ified by xµ = (x0; ~x); ~x = (x1; x2; x3); x0 = ct: (1) This is saying that we will take the familiar 3-vector ~x and regard its three components as part of the 4-vector. What we often call x is now x1; y is x2; and z is x3: Together with x0 ≡ ct; these make up the basic space-time 4-vector. In special relativity, we need to distinguish upper and lower indices. So along with µ x we also have xµ; specified by 0 xµ = (x ; −~x) µ The scalar product of a 4-vector with itself involves both x and xµ: We define µ 0 2 x · x = xµx = (x ) − ~x · ~x; (2) µ where the convention is that repeated upper and lower indices are summed, so xµx really means X3 µ xµx µ=0 µ More formally, the relation between xµ and x can be written using the metric tensor gµν; ν xµ = gµνx ; or equivalently, µ µν x = g xν; where again there is a sum on the repeated index ν: By making use of Eq.(2) we find that the components of gµν are given by 8 > > g00 = 1 > <> − gµν : > gkk = 1 ; > > :> gµν = 0; µ =6 ν µν and further that gµν = g : It is easy to remember the rule for raising and lower indices; for a 0 or time index, raised and lowered versions are the same, whereas for a spacial 1 index (1,2,3), raised and lowered versions differ by a minus sign, e.g.
    [Show full text]
  • On Fractional Schrödinger Equation and Its Application
    International Journal of Scientific & Engineering Research Volume 4, Issue 2, February-2013 1 ISSN 2229-5518 On Fractional Schrödinger Equation and Its Application Avik Kumar Mahata Abstract— In the note, recent efforts to derive fractional quantum mechanics are recalled. Time-space fractional Schrödinger equation with and without a Non Local term also been discussed. Applications of a fractional approach to the Schrödinger equation for free electron and potential well are discussed as well. Index Terms— Caputo Fractional Derivative, Fractional Calculus, Fractional Schrödinger Equation, Space Time Fractional Schrödinger Equation, Time- Space fractional Schrödinger like equation, Free Electron, Potential Well. 1. INTRODUCTION Specifically, they present the model of a hydrogen- The fractality concept in Quantum Mechanics like fractional atom called “fractional Bohr atom.” developed throughout the last decade. The term fractional Quantum Mechanics was first introduced Recently Herrmann has applied the fractional by Laskin [1]. The path integrals over the Lévy mechanical approach to several particular problems paths are defined and fractional quantum and statistical mechanics have been developed via new [7-12]. Some other cases of the fractional fractional path integrals approach. A fractional Schrödinger equation were discussed by Naber [13] generalization of the Schrödinger equation, new and Ben Adda & Cresson [14]. relation between the energy and the momentum of non-relativistic fractional quantum-mechanical particle has been established [1]. The concept of 2. FRACTIONAL CALCULUS fractional calculus, originated from Leibniz, has gained increasing interest during last two decades (see e.g. [2] and activity of the Fracalmo research Fractional Calculus is a field of mathematic group [3]). But the concept of fractional calculus was study that grows out of the traditional definitions of originally introduced by Leibniz, which has gained special interest in recent time.
    [Show full text]
  • Scattering and S-Matrix 1/42 J
    SCATTERING AND S-MATRIX 1/42 J. Rosner – Reaction Theory Summer Workshop Indiana University – June 2015 Lecture 1: Review of Lecture 2: S-matrix and Lecture 3: Some simple scattering theory related physics applications S, T , and K matrices 1-,2-channel examples Optical analogs Wave packet scattering Transmission resonances Eikonal approximation Scattering amplitude Bound states Diffractive scattering Partial wave expansion S wave properties Adding resonances Phase shifts Resonances Dalitz plot applications R-matrix Absorption Historical notes Unitarity circle Inelastic cross section Example from electronics For simplicity some of the formalism will be nonrelativistic “In” state i : Free particle in remote past | iin “Out” state j : Free particle in remote future outh | S-matrix takes “in” states to “out” (with wave packets: Goldberger and Watson, Scattering Theory, 1964.) UNITARITY; T AND K MATRICES 2/42 Sji out j i in is unitary: completeness and orthonormality of “in”≡ andh | i “out” states S†S = SS† = ½ Just an expression of probability conservation S has a piece corresponding to no scattering Can write S = ½ +2iT Notation of S. Spanier, BaBar Analysis Document #303, based on S. U. Chung et al. Ann. d. Phys. 4, 404 (1995). Unitarity of S-matrix T T † =2iT †T =2iT T †. ⇒ − 1 1 1 1 (T †)− T − =2i½ or (T − + i½)† = (T − + i½). − 1 1 1 Thus K [T − + i½]− is hermitian; T = K(½ iK)− ≡ − WAVE PACKETS 3/42 i~q ~r 3/2 Normalized plane wave states: χ~q = e · /(2π) 3 3 i(~q q~′) ~r 3 (χ , χ )=(2π)− d ~re − · = δ (~q q~ ) . q~′ ~q − ′ R Expansion of wave packet: ψ (~r, t =0)= d3q χ φ(~q ~p) ~p ~q − where φ is a weight function peaked aroundR 0 3 i~k ~r Fourier transform of φ: G(~r)= d k e · φ(~k) 3 R ψ~p(~r, t =0)= d q χ~q ~p+~p φ(~q ~p)= χ~p G(~r) .
    [Show full text]