Questions tagged [initialization]

For questions regarding the initial state of a system for quantum computation and their preparation.

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What are the mathematics and theory behind Initializing a quantum state vector?

I do not understand how the initialize function in QiSkit is working. I know that it is used to put a qubit in a specific custom state. My question is - how is it implemented or how to do such a thing ...
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2 votes
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From the final quantum state to the quantum circuit composition

When I build a quantum circuit and my initial state is the one composed only by zeros ($|000\ldots 0\rangle$), I have a final state $|\psi\rangle$ that is the result of the application of the quantum ...
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How to separate initializing qubits from runing algorithm several times

I have read several papers about quantum computing. It looks like any algorithm consists of several phases. For example in Grover algorithm initially qubits must be initialized from reset state $|0\...
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How is the state preparation Unitary in initialize selected?

Normally, in order to prepare the Bell state $\frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)$, we can simply make a circuit with a Hadamard gate on $|0\rangle$ followed by a CNOT gate on $|1\rangle$. ...
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Setting the Initial State of Density Matrix Simulation in Cirq

I am trying to use the DensityMatrixSimulator in Cirq. I want to append gates to the circuit conditional on measurements. In order to reduce computational resources, I am trying to run these ...
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Why wont my custom controlled gates in Cirq work on a simulator?

To initialize a state in Cirq, I created a custom controlled rotation and a custom rotation gate. The effect of applying the custom controlled gates to the qubits doesn't seem to affect the state. ...
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2 votes
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Using QuantumCircuit.initialize() on a real quantum computer

Can the qiskit function QuantumCircuit.initialize be used to initiate any number of qubits (which exist currently on the quantum computers) and can it be used on a real quantum computer?
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Qiskit: Initializing $n$ qubits with binary values ($0$s and $1$s)

Is there a way in Qiskit to initialize $n$ qubits with binary values (0s and 1s)? For example, how can I initialize two qubits in the state $|11\rangle$? Here is a code snippet: ...
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3 votes
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Why after transpiling a Qiskit circuit we obtain a different result?

I am trying to obtain the correct circuit transpiled for the ibmq_london device, as I want to know what the real gates applied in the quantum computer are. I am implementing the QFT circuit for 5 ...
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3 votes
2 answers
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Is there a "parameterized initialization" that I can apply to a QuantumRegister to re-use a circuit?

I'm working on a QuantumCircuit which measures the fidelity of one point (my "test vector") and two other points (my "data set", containing of states phi_1 and <...
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How can I initialize a state with chosen amplitudes in Qiskit?

I was trying to initialize to an arbitrary state of n qubits with the initialize() from Qiskit but it doesn't generate a state with the same amplitudes passed as an ...
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VQE restart from a previous computation

I'm running VQE algorithm on ibmq-qasm-simulator. I'm trying to implement a restart mechanism in order to be able to start a new computation from the result of a ...
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1 answer
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Prepending initial state to a quantum circuit in Qiskit

I am trying to generate a Quantum Phase Estimation (QPE) circuit in QISKIT the following way. 1 - First, I generate a QPE circuit with the following code: ...
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3 votes
1 answer
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How to pick number of simulation qubits for finding eigenvalue of fermionic Hamiltonian?

I am having some trouble understanding how the number of simulation qubits are chosen when finding the eigenvalue of a fermionic Hamiltonian. For the phase-estimation algorithm, is the number of ...
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1 answer
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Default value for a state created by QuantumRegister

What's the default value for a state created by QuantumRegister(1,'name_of_the_register')? Is it a $|0\rangle$ or a $|1\rangle$?
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1 answer
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Default input states of qubits to quantum circuits [closed]

It is conventional to assume that the state input to the circuit is a computational basis state, usually the state consisting of all $|0\rangle$s. This rule is broken frequently in the literature ...
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6 votes
0 answers
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Projective measurements: aftermath and restoration

I have some practical difficulties with projective measurements, so I'd welcome inspiration from others. This is beyond the question "Are true Projective Measurements possible experimentally?" in that ...
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6 votes
1 answer
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Threshold and practical requirements for initial state preparation?

At the beginning of a quantum computational process we generally want to start in a perfectly known initial state, and evolve from there. This cannot be done perfectly, for fundamental reasons, but I ...
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