Bra-ket notation to Matrix for entangled pairs

Click For Summary

Discussion Overview

The discussion revolves around the interpretation of bra-ket notation for entangled pairs, specifically the notation |ab> and its relationship to the tensor product |a> ⊗ |b>. Participants explore the application of the Hadamard operator to quantum states, particularly in the context of entangled qubits and the implications of applying the operator multiple times.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about whether |ab> is equivalent to |a> ⊗ |b> for entangled pairs.
  • Another participant confirms the equivalence but notes ambiguity in the application of the Hadamard operator to the state |01>.
  • Concerns are raised about the interpretation of applying the Hadamard operator twice, questioning if it means (H|0>) ⊗ (H|1>) or H(H(|01>).
  • A participant suggests that the language used could be clearer, particularly regarding which qubit the Hadamard transformation is applied to.
  • It is mentioned that to apply the transformation to a single qubit in a two-qubit system, one must use a specific notation involving tensor products of matrices.
  • Questions are posed about the effects of applying the Hadamard matrix twice in succession, considering its properties as symmetric and unitary.

Areas of Agreement / Disagreement

Participants generally agree on the equivalence of |ab> and |a> ⊗ |b>, but there is disagreement and confusion regarding the application of the Hadamard operator and its implications for the state |01>.

Contextual Notes

The discussion highlights ambiguities in the language used to describe quantum operations and the need for clarity regarding which qubit is being transformed. There are unresolved questions about the mathematical representation of the states and operators involved.

Who May Find This Useful

Individuals interested in quantum mechanics, particularly those studying quantum computing and entanglement, may find this discussion relevant.

nomadreid
Gold Member
Messages
1,773
Reaction score
256
I am confused about the the notation |ab> for an entangled pair. Isn't this the same as the tensor product |a> \otimes |b>? If so, I run into another confusion when using the corresponding matrices. I read that I should apply a Hadamard operator H twice to the input state |01>. Does this mean (H|0>)\otimes (H|1>)? I don't see how it could mean H(H(|01>), since |01> is represented by a four-by-one matrix, whereas H is represented by a two-by-two matrix. So what does this mean? Thanks
 
Physics news on Phys.org
No, unfortunately.
 
nomadreid said:
I am confused about the the notation |ab> for an entangled pair. Isn't this the same as the tensor product |a> \otimes |b>?
Yes.

nomadreid said:
If so, I run into another confusion when using the corresponding matrices. I read that I should apply a Hadamard operator H twice to the input state |01>. Does this mean (H|0>)\otimes (H|1>)? I don't see how it could mean H(H(|01>), since |01> is represented by a four-by-one matrix, whereas H is represented by a two-by-two matrix. So what does this mean?
The statement is ambiguous. The use of the word "twice" mean for me that the same thing has to be done two times. If you were to apply a Hadamard transformation to both qubits, the language would be different, I think. However, what is not said is which qubit the Hadamard transformation must be applied to.

To apply the transformation to a single qubit in a two-qubit system, one must use ##H_1 \otimes 1_2## where the subscript refer to which qubit is operated on. In matrix form, this is a 4x4 matrix.

That said, the Hadamard matrix is symmetric and unitary. What happens when it is applied twice in row?
 
  • Like
Likes   Reactions: Greg Bernhardt

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
Replies
7
Views
3K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K