In general, the expectation values of observable quantities depend on time. In quantum mechanics, these values are given by the expression: 10.1 https://www.w3.org/1998/Math/MathML" display="block"> < X > t = < A ( t ) | X ( t ) | A ( t ) > . https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003436263/11a1814b-c2ab-4d89-be15-80efb520b7b3/content/math10_1.tif "/>
The n -puzzle is a classical problem for modeling algorithms. For n -puzzle there are https://www.w3.org/1998/Math/MathML" display="inline"> n + 1 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_1.tif "/> different objects: n cells and one empty cell. Each object can be coded by https://www.w3.org/1998/Math/MathML" display="inline"> ρ = ⌈ log 2 n + 1 ⌉ https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_2.tif "/> qubits and a configuration of https://www.w3.org/1998/Math/MathML" display="inline"> n + 1 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_3.tif "/> objects can be represented by a register of https://www.w3.org/1998/Math/MathML" display="inline"> z := ρ ⋅ ( n + 1 ) https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_4.tif "/> qubits https://www.w3.org/1998/Math/MathML" display="inline"> | x ⟩ https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_5.tif "/> . The function https://www.w3.org/1998/Math/MathML" display="inline"> g ( x ) https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_6.tif "/> is represented a unitary operator T . T acts on the https://www.w3.org/1998/Math/MathML" display="inline"> z + 1 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_7.tif "/> qubits with https://www.w3.org/1998/Math/MathML" display="inline"> x ∈ B z https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_8.tif "/> and https://www.w3.org/1998/Math/MathML" display="inline"> c ∈ B 1 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_9.tif "/> https://www.w3.org/1998/Math/MathML" display="block"> T ⋅ | x ⟩ | c ⟩ = | x ⟩ | f ( x ) ⊕ c ⟩ . https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003374404/4745344c-4074-4386-85e6-ca8a3849de1f/content/math10_10.tif "/>
In general, the expectation values of observable quantities depend on time. In quantum mechanics, these values are given by the expression: < X >t=< A(t)|X(t)|A(t) >. (10.1) There is an intrinsic ambiguity in determining the time dependence on the various elements (bra, ket and operator) which comprise the right hand side of equation (10.1) because we can transfer this dependence from one element to another, while keeping unchanged the expectation value < X >t, which is all we can measure on the system. The ambiguity gives rise to different descriptions of the motion, connected to unitary time-dependent transformations, thus equivalent to each other. In the following sections, we describe the Schro¨dinger and Heisenberg representations. Subsequently we will introduce a third description of the motion or interactions: the Dirac representation, also called the interaction representation, which is particularly useful in the case of weakly interacting systems.
The dynamics of a quantum system is governed by the Hamiltonian H^.If∣Ψ⟩ is a quantum state of the system in an abstract Hilbert space representation, its time-evolution is given by −iℏ∂t∂∣Ψ⟩=H^∣Ψ⟩ (1.1)
In this chapter we are going to explicitly identify the parameter, t , from Chapter 4 as a continuous variable that corresponds to time in a physical system. This will enable us to show how natural number dynamics can be converted into Hamiltonian form and thus develop dynamical equations that can be applied to physical systems, that form the basis for standard quantum mechanics. It is instructive to begin with a single category system with n items. We will take the system to be bosonic so that n can be any natural number. We then simply parameterize the variable ξ with t , as we did for the multi-category case, by writing https://www.w3.org/1998/Math/MathML" display="inline"> ξ = ω 0 t https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003377504/0865e0f9-b6f9-4666-9620-3b3ea10ce510/content/math5_1.tif "/> , where ω 0 , is a constant angular frequency. Eq. (3.14) can then be transformed into a time evolution S-type equation applied to an eigenfunction, https://www.w3.org/1998/Math/MathML" display="inline"> Φ n https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003377504/0865e0f9-b6f9-4666-9620-3b3ea10ce510/content/math5_2.tif "/> of the operator https://www.w3.org/1998/Math/MathML" display="inline"> N ^ https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003377504/0865e0f9-b6f9-4666-9620-3b3ea10ce510/content/math5_3.tif "/> . Comparing the result with Eq. (4.9) , one then gets 5.1 https://www.w3.org/1998/Math/MathML" display="block"> i d Φ n d t = Ω ^ Φ n = ω 0 N ^ Φ n , https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003377504/0865e0f9-b6f9-4666-9620-3b3ea10ce510/content/math5_4.tif "/>
In this chapter, the simplest quantum measurement situation, i.e., where the state is an eigenvector of the observable to be measured, is considered. The states are therefore non-superimposed and measurement Axiom 3.2 of Section 13.7 in the previous chapter is applicable. We consider states in https://www.w3.org/1998/Math/MathML" display="inline"> ℂ 2 , ℂ 2 ⊗ ℂ 2 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003264569/7139ce19-0d58-4a0c-820f-b76fb033e438/content/math14_1.tif "/> and https://www.w3.org/1998/Math/MathML" display="inline"> ℂ 2 ⊗ ℂ 2 ⊗ ℂ 2 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003264569/7139ce19-0d58-4a0c-820f-b76fb033e438/content/math14_2.tif "/> . The generalisation to https://www.w3.org/1998/Math/MathML" display="inline"> ⊗ n ℂ 2 https://www.w3.org/1999/xlink" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003264569/7139ce19-0d58-4a0c-820f-b76fb033e438/content/math14_3.tif "/> is then clear.