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Some of the qubits are not evaluated at Qiskit

When I implement a 3-qubit circuit in Qiskit, circuit is executed smoothly at the simulator but counts I read back as results does not contain all of the qubits that are defined and included in the ...
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-1 votes
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56 views

PhD topics in quantum computing

I am looking for PhD topics in quantum computing related to computer Engineering background (I don't have a background in physics). I tried searching for Machine learning, neural networks and Quantum ...
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2 votes
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30 views

Barren Plateau as a consequence of 2-desgin?

Initializing a parameterized quantum circuit with a unitary sampled from a uniform distribution (so sampling from the Haar distribution) or in a weaker form: a unitary which is a unitary 2-desgin, ...
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2 answers
33 views

Expected Minimum Clique Coverage?

I'm curious if there is literature on this and, if there is, where to find it. Here I'm using ``clique" to mean a set of observables which all commute with each other. I also include the identity ...
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2 votes
1 answer
26 views

T-depth in Qiskit

How to find T-depth in Qiskit? Is there any inbuilt function or some method to find T-depth? I know that the .depth() function exists which returns circuit depth (i....
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1 vote
1 answer
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Qiskit: How to implement a classical function?

I'm quite lost, I have to implement the following function with qiskit $$ f(x,y,z) = (\lnot x \land y \land z) \lor (x \land \lnot y \land z) $$ but how can we do that ? I don't understand how to do ...
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2 answers
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qiskit qaoa.compute_minimum_eigenvalue

I am having some trouble running the compute_minimum_eigenvalue method from qiskit's QAOA: the documentation states that one ...
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-1 votes
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12 views

Are there hardware platforms that natively implement parametric two qubit gates?

For example, is it possible to implement RXX gate with an arbitrary angle on an ion computer in a single native operation? The RXX gate with an arbitrary angle can be decomposed into two RXX gates ...
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9 votes
1 answer
242 views

Is there a closure property for the entire Clifford hierarchy?

TL;DR Is the entire Clifford hierarchy (as opposed to any one level), a group? Background. The Clifford hierarchy (on $n$ qubits), is a collection of nested subsets $\mathcal C^{(1)} \subset \mathcal ...
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70 views

Reshaping the 4x4 CNOT gate into 2x2x2x2 in a tensor network

I'm learning how to perform tensor network contraction for simulating a quantum circuit by looking at the documentation for the JET simulator: link. Specifically, I'm trying to do all the calculations ...
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  • 11
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0 answers
25 views

Performance metrics in QSVM

I have implemented QSVM on breast cancer dataset using link: "https://qiskit.org/documentation/stable/0.24/tutorials/machine_learning/01_qsvm_classification.html" but unable to compute other ...
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1 vote
2 answers
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How to calculate eigenvalues by phase estimation?

I have been learning Quantum PCA recently but I came across a problem. How can I get the eigenvalues of a matrix by phase estimation? And what on what kind of matrix can we implement this algorithm?(...
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Expectation value of Pauli string for VQE

One approach to get the expectation value $\langle\psi|P\psi\rangle$ of a pauli string $P\in \{I, X, Y, X\}^{\otimes n}$ is the following. Let $(a_i, |\lambda_i\rangle)$ be eigenvalue-eigenvector ...
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1 answer
39 views

What role does Landauer's principle play in quantum reverisbility?

In section 3.2.5 of Nielsen and Chuang (starting page 153) they talk about Landauer’s principle, where they discuss the lower bound on the thermodynamic cost of erasing information. In irreversible ...
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2 votes
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Predator–prey theory

We have a project where we are supposed to simulate the predator–prey theory in qiskit. Can anyone help or suggest of any ways to start from somewhere because we are kinda lost.
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3 votes
2 answers
47 views

Why should we purify a mixed state?

I'm new to quantum computing so I know this question may sound stupid. But I still want to know why purification is necessary sometimes. Please help me with it:)
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0 answers
31 views

Conditional measurement using classical bit in qiskit

I am trying to implement Figure 6 in Implementing a distance-based classifier with a quantum interference circuit by Schuld et. al The specific part that I'm struggling with is the controlled (on |0&...
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3 votes
1 answer
156 views

Are the pure quantum states that make up a mixed state orthogonal?

I came a cross a problem when leaning Quantum PCA. I know that a mixed state is an ensemble of several quantum states. But I wonder whether these states that make up for the mixed state are orthogonal....
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2 votes
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contraction related Bit flip channel

Studying the bit flip channel using the Nielsen & Chuang's. And ran into the picture with the caption stating y-z plane is uniformly contracted by a factor of 1-2p. I don't quite understand how ...
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1 answer
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Qiskit: Transpile circuit with custom equivalences

I would like to automatically get a phase gate of pi/2 converted to a S gate. I have: ...
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0 votes
1 answer
21 views

Converting data into a SHA256 hash using Qiskit quantum computer

I was wondering how can we convert data into a hash using Qiskit quantum computer? e.g, this code below will generate a SHA256 hash based on random data. ...
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0 answers
13 views

Is there a way to connect a IBM quantum lab code to an Unreal Engine project?

I would like to know whether someone tried this before, I'm interested in be able to connect this tools. I know that Unreal Engine has a plugin to program with python, that all I know. I'll really ...
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2 votes
0 answers
24 views

Decomposing S gate in two T gate with qiskit

Let's suppose I define a basis gate set and the following circuit. ...
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3 votes
2 answers
71 views

Is a "Bell measurement" equivalent to a projective measurement in a different basis?

Let \begin{align} H = \frac{1}{\sqrt{2}}\begin{bmatrix} 1 & 1 \\ 1 & -1\end{bmatrix}\in M_2(\mathbb C), \quad \mathrm{CNOT} = \begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 &...
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0 answers
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Usage of slack variables by Dimod (D-Wave)

I have a general question of the application of slack variables. For example, if I want to solve the following inequality: $x_{0}+x_{1}+x_{2}+x_{2} \leq 2$ Then I can reformulate the inequality above ...
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1 vote
1 answer
153 views

Why do we have only 3 Pauli gates X, Y and Z

This question is out of curiosity thus might not be of much importance. We have Pauli X, Y, Z gate which rotate the phase by π along X, Y and Z basis. Just wondering why not do we have these 3 gates ...
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1 vote
2 answers
28 views

How is the ket of a quantum state calculated in this code?

For the following code qc = QuantumCircuit(2) qc.h(1) qc.cx(1,0) ket = Statevector(qc) ket.draw() the output will be the following: ...
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3 votes
0 answers
27 views

How is this Variational Quantum Singular Value Decomposition paper efficient in any way?

Link to paper here. This algorithm seems neat but the unitary decomposition of the matrix M generally takes an exponential number of Pauli basis elements in the number of qubits $N$, therefore an ...
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2 votes
1 answer
45 views

What is the difference between $|+\rangle$ and $|-\rangle$?

What is the difference between $|+\rangle$ and $|-\rangle$. I was reading about quantum states and found that $|+\rangle$ and $|-\rangle$ represent state in superposition of other states. I was just ...
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1 vote
1 answer
41 views

What is the original paper introducing the Variational Quantum Eigensolver?

My question is very simple. I am looking for original paper where Variational Quantum Eigensolver (VQE) has been introduced. After some Googling I was able to find many applications of VQE and its ...
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0 votes
1 answer
29 views

How to calculate parameters of U3 gate from a certain quantum state?

I'm trying to do Quantum PCA but I came across a problem. I now have a quantum state, say $\frac{|00\rangle+|01\rangle+|11\rangle}{\sqrt{3}}$ and I want to know how to prepare it from two $|0\rangle$ ...
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2 votes
2 answers
126 views

Why can the CNOT representation $e^{i\frac{\pi}{4}\left(I-Z\right)\otimes\left(I-X\right)}$ hardly be found in books?

The CNOT gate is usually written as $|0\rangle\langle0|\otimes I + 1\rangle\langle1|\otimes X$ (with $X,Y,Z$ being the Pauli Basis and $I$ the Identity). I have yet to stumble across the ...
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  • 121
2 votes
3 answers
89 views

Why do we need physical qubit if qubit can be simulated?

I do not see any advantage in constructing very costly and imperfect physical qubit while this qubit can be simulated with using conventional computer memory (noise-free). So what is the purpose when ...
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  • 354
2 votes
1 answer
27 views

Why does the condition $\langle \varphi _k\left( t \right) |\dot{\varphi}_l\left( t \right) \rangle =0$ called parallel transport condition?

I'm reading this paper about nonadiabatic holonomic quantum computation and met the condition eq.(2) states that $\langle \varphi _k\left( t \right) |\dot{\varphi}_l\left( t \right) \rangle =0$ is the ...
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  • 533
0 votes
0 answers
18 views

How to use QubitConverter and ParityMapper to do chemistry simulation?

After viewing the question: Hamiltonian & QubitMappingType cannot be imported from qiskit.chemistry.core, I also want to implement the same Jupyter notebook and browsed the response below. However,...
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2 votes
1 answer
28 views

Oracle for amplitude addition

Assume one is given two oracle circuits providing access to matrices $A_{ij}$ and $B_{ij}$ as follows (see eq. (6.2) here): \begin{equation} O_A |0\rangle|i\rangle|j\rangle=\left(A_{ij}|0\rangle+\sqrt{...
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  • 1,408
1 vote
1 answer
55 views

Computing characteristic polynomial of unitary operation

I am trying to replicate a calculation from the linked paper but I am unsure if I understand their math. A locally invariant function defined as the characteristic polynomial is as follows: $$F_U(t) = ...
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1 vote
0 answers
19 views

How to set the meas_level and optimization_level in Quantum Azure IonQ provider?

I am performing a benchmark process using the Azure Quantum IonQ provider. I use Qiskit in the Azure platform, and I was trying to see how to control the transpiling and compiling process. It seems ...
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  • 254
0 votes
1 answer
35 views

ket statevector of a 2-quibit system

Given the following code: ...
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0 votes
1 answer
46 views

What is $j$ in the state $|\psi\rangle=\sqrt{(1-p)}|0\rangle + e^{j\phi}\sqrt{p}|1\rangle$?

What is the j in the single qubit state equation in the Quantum Phase section? https://quantum-computing.ibm.com/composer/docs/iqx/guide/introducing-qubit-phase it's not defined in the page itself (...
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0 votes
2 answers
45 views

Expectation value of pauli strings for VQE

I am studying VQE and have boiled it down to a matter of determining the expectation value of pauli strings: $$\langle H \rangle = \sum_i \alpha_i \langle\psi|\hat{P_i}|\psi\rangle.$$ I have been ...
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0 votes
1 answer
44 views

How to retrieve a quantum state after passing through a series of quantum gates?

Consider a qubit $$\left| \psi \right> = (\alpha_1 + i\alpha_2 ) \left|0\right> + (\beta_1 + i\beta_2 )\left|1\right>$$ Now if i pass this through a series of quantum gates or any typical ...
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1 vote
2 answers
48 views

Can I Convert a Qubit in complex form to polar form?

Let's say I have a qubit $$\left| \psi \right> = (\alpha_1 + i\alpha_2 ) \left|0\right> + (\beta_1 + i\beta_2 )\left|1\right>$$ Can I able convert this to polar form $$|\psi \rangle = \cos\...
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0 votes
0 answers
23 views

Grover search with index register entangled with ancilla

I have a question: when Grover's search is set up with ancilla qubits in an entangled state, does it still work or not? Consider an example with a 4-size search space. Firstly, we use 2 qubits ...
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1 vote
1 answer
33 views

How does an $\sqrt{X}$ error propagates through an $T$ gate?

I wonder whether there is a compact way of describing a noise $\sqrt{X}$ propagating through a $T$ gate. Possibly in terms of Pauli and/or Clifford operators.
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0 answers
14 views

Computational Complexity of random Transverse-Ising Chain

It is well known that many NP-hard classical problems can be mapped to a spin-configuration Ising problem (see for example https://arxiv.org/pdf/1302.5843.pdf) However, what I would like to know is ...
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0 votes
0 answers
58 views

Hamiltonian & QubitMappingType cannot be imported from qiskit.chemistry.core

I'm trying to implement the same Jupyter notebook in The Variational Quantum Eigensolver — Programming on Quantum Computers — Coding with Qiskit S2E4;however,I found a problem: Error: ...
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1 vote
2 answers
44 views

What does distinguishability mean in this case?

In a lecture, we were given the following example to explain the operational significance of the trace distance. Suppose that Alice prepares one of two (known) states $\rho_0$ or $\rho_1$ with equal ...
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  • 173
2 votes
0 answers
51 views

Is there a relation between quantum entanglement and inclusion-exclusion principle?

If an entangled state is not simply the multiplication of each particle wave function: $$ |\Psi_{ABC}\rangle \neq |\Psi_{A}\rangle|\Psi_{B}\rangle|\Psi_{C}\rangle $$ then can we apply the inclusion ...
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8 votes
2 answers
2k views

Why doesn't Shor's algorithm output a solution for some numbers?

I've been trying to mess around with Qiskit's implementation of Shor's algorithm, and while trying I've noticed that Shor(33), for example, would not output a solution (even with an absurd number of ...
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