# All Questions

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### Definition(s) of $\delta$ in quantum phase estimation

I read the chapter on QPE (quantum phase estimation) in Nielsen and noticed that $\delta$ is defined there as follows: $0 \leq \delta \leq 2^{-t}$, see: 5.2.1 Performance and requirements The above ...
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### Understanding Qiskit's $\texttt{AmplificationProblem()}$ behaviour

This is related to my previous question. To apply amplitude amplification in Qiskit, one needs to use AmplificationProblem() or ...
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### How we can show Lindblad operators are satisfying the following condition?

How can we show that when the Lindblad operators satisfy the condition: $$\sum_{\mu}L_{\mu} L_{\mu}^{\dagger} = \sum_{\mu} L_{\mu}^{\dagger}L_{\mu},\tag{1}$$ the master equation evolution ...
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### How to return phase angles as seen in IBMQ composer using qiskit?

I recently transitioned from using the IBMQ composer and am using qiskit in the IBM lab. To start, I wanted to learn how to reproduce the computational basis states, probabilities and phase angles as ...
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### What is the method to create arbitrary controlled circuits in Qiskit?

I am working on an implementation of an algorithm which uses ampitude estimation and amplification as a subroutine but we are not using qiskit but QuEST. QuEST doesn't have any direct method to ...
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### queueinfo() module in Qiskit

I want to know how to use queueinfo() module in IBM Qiskit. When I type job.QueueInfo(), it says "QueueInfo" is not defined. How to import it? I'm trying to use queueinfo() to know the time ...
47 views

### Setting the $\texttt{state_preparation}$ for $\texttt{AmplificationProblem()}$ in the scope of Grover's algorithm

I am having trouble setting the state_preparation parameter of AmplificationProblem() from ...
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### Is it possible to set quantum volume in IBM Quantum simulator?

A quantum volume serves as a metric of a quantum processor quality. So far, IBM Quantum provides processors with quantum volume up to 128. Freely accessbile processors have QV up to 32. A user using ...
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### Is the boundary of the set of quantum behaviours a polytope?

Consider the standard 2-2 Bell scenario, with two parties each one choosing between two measurement settings, with each measurement setting leading to one of two possible measurement outcomes. ...
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### What is the difference between quantum "system", "register" and "Hilbert space"?

As far as I can tell, these terms are interchangeable but I am not sure of this. What is meant by each of the terms "quantum system", "quantum register" and "Hilbert space&...
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### Why does $H^2=X^2 =I$ not imply $H=X$?

if $HH = I$ and $XX =I$, then is $H=X$? $HH = I = XX$ or, $HH = XX$ then, taking under root, is $H = X$? This is absurd but how to disprove it?
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### Are $(|00\rangle-|11\rangle)/\sqrt2$ and $(|11\rangle-|00\rangle)/\sqrt2$ the same quantum state?

The state $(|00\rangle-|11\rangle)/\sqrt2$ is an entangled state. If we think about the state $(|11\rangle-|00\rangle)/\sqrt2$, is this also entangled, but with maybe a phase change? The above two can ...
42 views

### Factoring Decision Problem - why not in P? [closed]

Nielsen and Chuang, 10th Anniversary Edition, page 142, refers to the following (classical) computation problem: Given a composite integer m and L <m, does m have a non-trivial factor less than L? ...
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### Why doesn't this simpler teleportation idea work?

This circuit: The first (upper) qubit is the one we want to teleport, so could start it any state, call $\alpha|0\rangle+\beta|1\rangle$. Our goal is to teleport it to the third (bottom) bit. After ...
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### Accessing more than 5-qubit IBM Quantum Computer [duplicate]

I'm doing a university project related to Physics using IBM Qiskit. I want to know how to get access to Quantum Computers with more than 5-qubits (preferably more than 10 qubits)? My account ...
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### Why is Measurement Device Independent (MDI) Quantum Key Distribution (QKD) truly MDI?

This is a repost from a question I posted in the physics stack exchange I am having a hard time understanding why MDI-QKD is truly measurement device independent. My current vision is that Charlie (...
129 views

### Is Toffoli a fault tolerant transversal gate of the repetition code on bit-flip-error-only qubits?

Suppose you have physical qubits that only have bit flip noise (no phase flip noise, no unwanted measurements, no leakage, no amplitude decay, etc; just unwanted X rotations). Such qubits can be kept ...
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### Openfermion state transformation from Bravyi-Kitaev basis to occupation number

I'm working in the Bravyi-Kitaev basis implemented by the openfermion.bravyi_kitaev() function to find the ground state of a fermionic operator in the BK ...
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### What are the vertices of the no-signalling set $\mathcal{NS}$?

Consider the standard 2-2 Bell scenario, with two parties each one choosing between two measurement settings, with each measurement setting leading to one of two possible measurement outcomes. ...
39 views

### For the circuit below, could anyone explain the results I get?

This was sent to qasm_simulator, and the results look like: It seems qasm has added classical bits but why there are gates on the right side of the line. What do they mean? Also, what does the result ...
41 views

### Why does measurement in computational basis result in classic probability?

I am working on a problem related to finding the limits on the joint probability distributions/correlations of three or more quantum systems who share entangled states, after measurement. I have been ...
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### In "from qiskit import *" , how can I check the entire spectrum of imports available

In some codes, I have seen "from qiskit import QuantumCircuit, aer, execute". Some say "From qiskit import *". This is python related, I understand, but with respect to Quantum ...
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### How can I add readout error in constructing a quantum noise model?

I'm trying to construct a quantum noise model with readout error only: qiskit.providers.aer.noise.NoiseModel.add_readout_error. However, when I try to specify the ...
46 views

### Hamiltonian of Qiskit QFT is not hermitian

I am trying to generate the Hamiltonian of a quantum Fourier transform by taking the log of the corresponding unitary using qiskit and scipy. I don't find a hermitian matrix. Why? ...
32 views

### Soundness of Grover's search application

I find that some algorithms can be sped up using Grover's search, but I have a question about the soundness of new algorithms. Since Grover's search is a probabilistic method, it has a chance to make ...
56 views

### Register size in factoring 15 using Shor's algorithm

In Nielsen and Chuang's book: Quantum computation and quantum information (2016), there is an example in Box 5.4 which shows how to factor $15$ using Shor's algorithm. I am confused about a ...
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### Derivation of efficiency of Phase Estimation Algorithm

In the section Performance and requirements of the phase estimation algorithm of Page 224, Quantum Computation and Quantum Information by Nielsen and Chuang In order to obtain Eq. 5.27 we have ...
23 views

### How do I construt a mixed state for an arbitrary symmetric matrix?

A symmetric matrix can be seen as a density matrix. If I have an arbitrary symmetrical matrix, can I use a quantum random access memory to construct a corresponding mixed state? What kind of quantum ...
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### Is there any software package tracking Pauli errors in stabilizing circuits with GUI?

I want to track the Pauli errors propagating in stabilizer circuits like surface code. I wonder whether there is any developed package that can do this elegantly. It will be better if it has GUI that ...
14 views

### Max-relative entropy quasi-convexity inequality under partial trace

The max-relative entropy between two states is defined as $$D_{\max }(\rho \| \sigma):=\log \min \{\lambda: \rho \leq \lambda \sigma\}.$$ It is known that the max-relative entropy is quasi-convex. ...
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### AttributeError: 'UCC' object has no attribute 'set_max_evals_grouped' [closed]

I'm trying to run the VQE algorithm using an Aer backend simulator. However, whenever I run the algorithm I Receive this error: "AttributeError: 'UCC' object has no attribute '...
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### Coupling maps in quantum computation

Perhaps a bit naive question from my side, but I could not find any satisfactory answer elsewhere: What exactly are the coupling maps in quantum computation and, more particularly, how do those maps ...
86 views

### Expected value of Z operator in GHZ state

I'm following this notebook written using amazon-braket, and there's a statement I don't understand ... To reiterate, the following output is expected: \left|\mathrm{GHZ}\right> = \frac{1}{\sqrt{...
908 views

### Why can't we simulate a Qubit using classical computer?

I am completely a noob in terms of quantum computing, have watched several videos to understand what Quantum computers are trying to achieve. I am a programmer of classical computers. We have a ...
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### VQE from scratch, what have I got wrong?

I've been working on a code to run VQE with a grouped measurement. For some reason, my expectation values are slightly off from those computed by pennylane, the software I decided to use for this ...
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### How should I think about circuit metrics like "qubit count," "circuit depth," and "gate count" when dealing with the OpenQASM 3 ctrl modifier?

It seems like circuit metrics like qubit count, circuit depth, and gate count are pretty useful. Qubit count determines whether a it's even possible to run a program on resource-limited quantum ...
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### Is it possible to use a quantum algorithm to optimize quantum chips

I'm really new to QC, so please excuse if this is a dumb question. I was looking at the different Qubit configurations/arrangments in chips and was wondering if it is possible to create an algorithm ...