Rewrite state in new basis - Quantum Mechanics

In summary, the given equations are rewritten in terms of the new basis |+⟩ and |−⟩, and the goal is to solve for |ψ⟩ in the new basis. By rearranging the equations, we can express | ↑⟩ and | ↓⟩ in terms of |+⟩ and |−⟩, and then solve for |ψ⟩ using substitution.
  • #1
12x4
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Homework Statement


Rewrite the state |ψ⟩ = √(1/2)(|0> + |1>) in the new basis.

|3⟩ = √(1/3)|0⟩ + √(2/3)|1⟩

|4⟩ = √(2/3)|0⟩ − √(1/3)|1⟩


You may assume that |0⟩ and |1⟩ are orthonormal.

Homework Equations



The Attempt at a Solution


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I have a similar example in my notes however there is a step that I has stumped me. Annoyingly its the first one.

In my notes I have:

"""If we want to work in the basis |+⟩ and |−⟩ instead of | ↑⟩ and |↓⟩, with,

|+⟩ = (1/√2)(| ↑⟩ + | ↓⟩) & |−⟩ = (1/√ 2)(| ↑⟩ − | ↓⟩)

how would |ψ⟩ and I be written in the new basis?

Let us rearrange as:

| ↑⟩ = 1/(√2)(|+⟩ + |−⟩) & | ↓⟩ = (1/√2)(|+⟩ − |−⟩)"""

After rearranging I think that I should be able to complete the question but as it stands I can't see how to rearrange them to get |0> & |1>. Any advice would be much appreciated as really struggling with Dirac notation at the moment. Thanks 12x4
 
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  • #2
You're probably just getting confused by the new notation. Consider the ordinary algebraic equations
\begin{align*}
u &= \frac{1}{\sqrt 2} x + \frac{1}{\sqrt 2} y \\
v &= \frac{1}{\sqrt 2} x - \frac{1}{\sqrt 2} y
\end{align*} How would you solve for ##x## in terms of ##u## and ##v##? You can essentially do the same thing.
 
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  • #3
thanks vela, I just managed to do it with your advice.
 

1. How do you rewrite a state in a new basis in quantum mechanics?

Rewriting a state in a new basis in quantum mechanics involves finding the coefficients of the new basis states that make up the original state. This can be done through various methods such as using transformation matrices or performing calculations using the inner product.

2. What is the significance of rewriting a state in a new basis in quantum mechanics?

Rewriting a state in a new basis allows us to express the same physical state in a different mathematical representation. This can be useful in simplifying calculations or gaining a better understanding of the system.

3. Can any state be rewritten in a new basis in quantum mechanics?

Yes, any state in quantum mechanics can be rewritten in a new basis as long as the new basis is complete and orthonormal. This is a fundamental concept in quantum mechanics and is known as the basis transformation property.

4. What are some common bases used in quantum mechanics?

Some common bases used in quantum mechanics include the position basis, momentum basis, energy basis, and spin basis. These bases are often chosen based on the physical properties of the system being studied.

5. How does rewriting a state in a new basis affect its physical properties in quantum mechanics?

Rewriting a state in a new basis does not change its physical properties. The state remains the same, but its representation in terms of the new basis states may be different. This is similar to changing the units of measurement for a physical quantity without changing its value.

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