Questions tagged [state-preparation]
a procedure that outputs repeated examples of the same quantum system - particle or multiparticle system - in the same quantum state
13
questions
5
votes
2answers
65 views
How many quantum gates are needed to prepare an arbitrary state?
In this paper there is this sentence:
[...] the description of a $2^n\times2^n$ unitary matrix $U$ (which is a poly($n$)-size quantum circuit)
According to the meaning of "which" in ...
3
votes
2answers
62 views
How to create superposition of states with fixed parity with a quantum circuit?
I'm searching for a circuit to generate, starting from the $|00\, ...\,0\rangle$ state, an arbitrary superposition of all states with either even or odd parity. The gate choice is irrelevant for now, ...
2
votes
1answer
70 views
How to create known quantum state in Qiskit (or any other platform) comprising of two or more bits?
Is there there any way to create a known quantum state in Qiskit (or any other platform) comprising of two or more than two bit?
For example if I want to create $\frac{1}{\sqrt{3}}[|00\rangle+|01\...
2
votes
1answer
144 views
Is the CNOT in the standard three-qubit circuit for the GHZ state necessary?
This is a very basic question about the GHZ state. I know the standard construction:
A Hadamard on one qubit, and then CNOT gates with targets on all the other ones.
However, why can't I just have $n$...
2
votes
0answers
104 views
How can a density matrix be prepared on a quantum register?
I am currently trying to implement the VQSE algorithm.
There the biggest eigenvalues and their corresponding eigenvectors of a density matrix $\rho$ are computed.
In contrast to VQE, the matrix $\rho$ ...
3
votes
2answers
66 views
How to prove that EPR outcomes have equal probability no matter the basis?
Recently in class, we learned about the EPR state. I know that no matter what basis the first qubit is measured in, the two outcomes have an equal probability. However, how does one prove this? I ...
3
votes
0answers
94 views
If we can prepare a ground state efficiently, when can we prepare the second-lowest energy eigenstate?
I'd like to know if there's anything that can be said about whether and when we can efficiently prepare a state corresponding to the second-lowest eigenvalue of a given Hamiltonian, or in any other ...
3
votes
1answer
87 views
How to prepare a random 1-qubit superposition for data encoding
Let's assume we have a normalized data vector $\vec{x}= [x_1,x_2]$. How can I prepare a state $$|\psi\rangle = x_1|0\rangle+x_2|1\rangle$$
for any $\vec{x}$. I know that this state is in general not ...
10
votes
1answer
253 views
Is there an efficient circuit implementing the unitary $U|x\rangle|0\rangle=|x\rangle\Big(\sqrt{1 - x/2^n}\,|0\rangle+\sqrt{x/2^n}|1\rangle\Big)?$
Given an $n$-qubit register $|x\rangle$, does there exist an efficient circuit implementing unitary operation $U$ such that
$$U |x\rangle|0\rangle = |x\rangle\Big(\sqrt{1 - x/2^n}\, |0\rangle + \sqrt{...
5
votes
2answers
92 views
How instantaneous is state preparation in a quantum register, if all possible superpositions are to be initialized equally?
Before the start of a quantum algorithm qubits need to be initialized into a quantum register. How fast can a quantum register of length $n$ be initialized in a way that all possible superpositions of ...
-3
votes
2answers
180 views
Have you ever seen the preparation of the state $a^{*}|0\rangle+b^*|1\rangle$ and $a|0\rangle+b|1\rangle$ from one initial state?
Have you ever seen the preparation of the state $a^{\star}|0\rangle+b^{\star}|1\rangle$ and $a|0\rangle+b|1\rangle$ from one initial state?
0
votes
1answer
120 views
Produce a quantum state with its density matrix an identity matrix up to an constant
For a n-qubit quantum state $|\psi\rangle=\displaystyle\sum_{i=0}^{2^N-1}|i\rangle$, by definition it's density matrix is $|\psi\rangle\langle\psi|=\displaystyle\sum_{i,j=0}^{2^N-1}|j\rangle\langle i|$...
2
votes
1answer
133 views
How can I find the fidelity of the preparation operation $|0\rangle$ of IBMQ?
I want to know the fidelity (or error rate) of the preparation of $|0\rangle$. How can I obtain it?
