Questions tagged [initialization]

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

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Initializing qubits in Ca$^+$ ion

In Chapter 13 of "Quantum Computing - From Linear Algebra to Physical Realizations" by Nakahara and Ohmi, there is a discussion about initializing qubits in a trapped Ca$^+$ qubit. The ...
grav.field's user avatar
4 votes
2 answers
109 views

Survey of which 'physically interesting' many-body states can be efficiently prepared on a quantum computer?

For digital quantum simulation of many-body problems, efficiently preparing an initial state of 'physical interest' (e.g. ground states, thermal states, topologically ordered states etc.) is very ...
lm1909's user avatar
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1 answer
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How to initialize a function in Qiskit with 3 qubit? [closed]

I would like to know how I can make an initialization with 3 qubits to get |000> ,|100> , |111> ( 1 qubit --> |000> , |ψ⟩ = |000⟩ ⊗ |100⟩ ⊗ |111⟩)
DatagGirl's user avatar
0 votes
2 answers
123 views

Reducing circuit initialization complexity

I'm encoding data into a QuantumCircuit via the Initialize method for QFTs. In doing this and transpiling for IonQ backends, I'm getting rather complex circuits. Is there a way to encode this data ...
Jonathan Ortega's user avatar
1 vote
2 answers
155 views

How to initialize a $n$ qubit system in this specific state

Basically, I have $2n$ qubits and I want to initialize them in the state $\frac{|\psi\rangle}{\lVert |\psi\rangle \rVert}$ where $$|\psi \rangle = \sum_{\mathrm{w}\in \{0,1\}^n}|\mathrm{w}\mathrm{w}\...
Giorgos Giapitzakis's user avatar
0 votes
3 answers
143 views

How to get precise angle values in Qiskit while using initialize() function to generate arbitrary quantum state?

Is there any way to get the quantum gate values more precisely in qiskit? For example, if I want to create 1/√3[|00⟩+|01⟩+|11⟩]. By using initialize() I get the following circuit by using the draw() ...
Masab Iqbal's user avatar
2 votes
1 answer
207 views

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 ...
Yousef Zook's user avatar
2 votes
1 answer
77 views

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 ...
stopper's user avatar
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1 answer
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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\...
nckm's user avatar
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6 votes
1 answer
388 views

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 $|1\rangle$. ...
sven's user avatar
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1 answer
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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 ...
lor's user avatar
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2 votes
0 answers
112 views

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. ...
user14860's user avatar
2 votes
1 answer
128 views

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?
AL_P's user avatar
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3 votes
5 answers
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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: ...
Dr. Prasanna Date's user avatar
3 votes
1 answer
878 views

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 ...
Paula G's user avatar
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4 votes
2 answers
124 views

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 <...
GroenteLepel's user avatar
1 vote
1 answer
418 views

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 ...
up6w6's user avatar
  • 21
2 votes
1 answer
244 views

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 ...
Valentina's user avatar
1 vote
1 answer
529 views

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: ...
NikPapadopoulos's user avatar
3 votes
1 answer
83 views

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 ...
QCQCQC's user avatar
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1 vote
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 $|1\rangle$?
user1319236's user avatar
-1 votes
1 answer
99 views

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 ...
Prasanth Kumar Vemula's user avatar
6 votes
0 answers
132 views

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 ...
agaitaarino's user avatar
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6 votes
1 answer
146 views

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 ...
agaitaarino's user avatar
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