How Does the Time-Dependent Schrödinger Equation Describe Qubit Evolution?

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SUMMARY

The discussion focuses on the application of the Time-Dependent Schrödinger Equation to determine the time evolution of a qubit's state, represented as |v(t)>. Given the initial state |v(0)> = \begin{pmatrix} 0 \\ 1 \end{pmatrix} and the Hamiltonian H = \begin{pmatrix} 0 & -iλ \\ iλ & 0 \end{pmatrix}, the eigenvalues are calculated as ±λ. The solution involves expanding |v(t)> in terms of the Hamiltonian's eigenstates and applying the time evolution operator e^{iHt/ħ} to derive the state at time t.

PREREQUISITES
  • Understanding of the Time-Dependent Schrödinger Equation
  • Familiarity with Hamiltonian mechanics
  • Knowledge of eigenvalues and eigenstates in quantum mechanics
  • Basic proficiency in complex numbers and exponential functions
NEXT STEPS
  • Study the derivation and application of the Time Evolution Operator e^{iHt/ħ}
  • Learn how to calculate eigenstates for a given Hamiltonian
  • Explore the concept of expansion coefficients in quantum state representation
  • Investigate the implications of qubit state evolution in quantum computing
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Students and researchers in quantum mechanics, particularly those focusing on quantum computing and the mathematical foundations of qubit evolution.

RJLiberator
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Homework Statement


Let |v(t)> ∈ℂ^2 by the time-evolving state of a qubit.
[tex]If |v(0)> =\begin{pmatrix}<br /> 0 \\<br /> 1<br /> \end{pmatrix}[/tex]
, and the Hamiltonian of the system is [tex]H = <br /> \begin{pmatrix}<br /> 0 & -iλ \\<br /> iλ & 0<br /> \end{pmatrix} (where λ∈ℝ)[/tex]
what is |v(t)>?

Homework Equations



Time dependent Schrödinger Equation:
iħ*d/dt(|v(t)>=H*|v(t)>

iħ*d/dt(α_j (t)) = α_j(t)*λ_j

The Attempt at a Solution



We just learned this material at the end of last lecture and I need to apply it to a couple final homework problems.

Overall, this seems like a straightforward computation but I'm severely struggling to decipher what I need to do with the giving material.

I first calculated the eigenvalues of the Hamiltonian as the teacher stated. This came out to be +/- λ.
Next, the teacher suggested expanding |v(t)> to something, I'm not really sure what he means by this.
What do the alphas represent? I have no idea... All I have is:
α_j (t) = α_j(0) e^(-iλ_i*t/ħ)

Can some please help me decipher this / lead me to start?

Thank you.
 
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RJLiberator said:
##
If |v(0)> =\begin{pmatrix}
0 \\
1
\end{pmatrix}
##
What does ##If## mean in the left hand side?
Anyway, apart from calculating the eigenvalues, you should also calculate the corresponding eigenstates of the Hamiltonian. Having found them, determine how the initial state ##v(0)## expands in term of these eigenstates, that is, try to find the expansion coefficients. The steps beyond this should be easy for you, to express the time evolution you simply need to apply the time evolution operator ##e^{iHt/\hbar}## to the initial state.
 
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