# All Questions

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### How to get state vector from QasmSimulator in Qiskit

I'm currently able to get state vector in Qiskit using state_vector backend using something like : ...
39 views

### Why running time of qasm simulator is significantly smaller in comparison with quantum machines?

I ran a 3-qubit measurement circuit on QASM simulator as well as on IBM Q Melbourne, Santiago and Vigo machines. The running time on the simulator is in few milliseconds (400-800) while in the case of ...
29 views

### Is there a measurable of entanglement for a macroscopic system?

After having a discussion with a quantum computing colleague, a question came up: is there any meaningful measure of entanglement in a macroscopic (i.e. many body) system where you don't have the ...
53 views

### What is the thought process for circuit making after seeing input and output of a matrix?

Here is an exercise (4.27) from Nielsen and Chuang and I found the answer (given in the figure below) online without any explanation. The question was to construct a circuit by seeing a matrix (given ...
27 views

### What is meaning of 'up to a global phase'? [duplicate]

What is the importance of global phase? How it affect a unit vector if we see it on a Bloch sphere? What is the meaning of 'up to global phase' in exercise 4.3 of Nielsen and Chuang?
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### Counting Achievable Operations

I'm struggling to find an analytic way to solve this problem. There are $4! = 24$ possible classical operations on the four 2-Cbit basis states. How many of these are achievable via the classical ...
30 views

### What is the significance of transpiling time, validating time, in queue time and running time?

What is the significance of different transpiling time, validating time, in queue time, running time for the same circuit run on different quantum systems for same no. of shots in IBM Q experience? ...
45 views

### Please explain this definition in an article about quantum error correction

I'm reading this article which is explaining about quantum error correction and fault-tolerance. I'm wonder what "Definition 1" means. Especially, "There is C is an ((n, K)) (binary) ...
42 views

### Give an explicit derivation of the formula for the two-qubit absolute separability Hilbert-Schmidt probability $\approx 0.00365826$

The two-qubit eigenvalue ($\lambda_i$ >= 0, $i=1,\ldots,4$, $\lambda_4=1-\lambda_1-\lambda_2-\lambda_3$) condition of Verstraete, Audenaert, de Bie and de Moor AbsoluteSeparability (p. 6) for ...
37 views

### Is it required to input full matrix when using Qiskit HHL algorithm for sparse matrices?

I am working with a very sparse matrix and it seems inefficient to load the full matrix as input into the Qiskit HHL algorithm. Is it possible to input only the non-zero elements, instead ? I am ...
38 views

### Quantum Circuit Optimization with Machine Learning

I read some paper about Quantum Circuit Optimization but I am on a low level. And have some experience in ML. But what I don't understand is it possible that ML can help to optimize Quantum Circuits ...
33 views

### Deformation of the Bloch sphere and contraction of its planes under the action of channels

On pg 376-377 of N&C, it gives 3 different diagrams showing how the various axis of the Bloch sphere will be contracted under the action of the channels, limiting the possible states after it's ...
98 views

### How to implement linear combination of two unitary gates in a quantum circuit?

I wanted to implement a non-unitary operation. I came to know that I can do it as a linear combination of unitaries from this paper (published version). Let us say I want to implement an operation ...
46 views

### Obtaining hermitian matrix using Knill and Laflamme condition?

Let $E$ be the set of all correctable errors and $E_a, E_b \in E$. Let $\lbrace \vert c_1\rangle, \vert c_2\rangle, \ldots \vert c_k\rangle\rbrace$ be the basis of codewords in the codespace. It is ...
54 views

### What would be measured if you measure two entangled qubits at exactly the same time?

What would be measured if you measure two entangled qubits at exactly the same time?
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### Splitting a quantum task between multiple devices

I've been wondering, are there any known tasks/algorithms that can be performed on 1 quantum device, but also be somehow modified and split between several smaller devices? The thought behind the idea,...
85 views

### Implementing a circuit that returns $|01\rangle$ and $|10\rangle$ with equal probability

Using Python how can I implement a quantum circuit that returns $|01\rangle$ or $|10\rangle$ using only $CX$, $RX$ and $RY$ gates, starting with random parametric gates as parameters and optimizing it ...
53 views

### Question on output of SWAP test

Let's say I have two arbitrary quantum states $|\psi\rangle$ and $|\phi\rangle$. I apply the SWAP test circuit (something like what is given here), and measure the first qubit to get either $0$ or $1$....
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### Can one use a quantum circuit as a pathfinding algorithm?

I've been learning about quantum computing, and I noticed that another way to describe the state vector is as a path in a binary tree where each level of tree represents another qubit, each node ...
33 views

### Secret string in least significant bit with Simon algorithm

The function $f:\{0,1\}^2\to\{0,1\}$ , $f(x_1x_0)=x_0$ returns the least significant bit of its argument. Solve the Simon's problem for this function and write down the number "a" (secret ...
85 views

### Google Colab - ImportError: The class MatplotlibDrawer needs pylatexenc

When I run the following command qc.draw(output='mpl') for my circuit qc, I get this error: ...
49 views

### Least significant bit with Simon algorithm

would you kindly help me solve this problem: The function $f:\{0,1\}^2\to\{0,1\}$ , $f(x_1x_0)=x_0$ returns the least significant bit of its argument. What is the $U_f$ operator for this function?
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### How to code a projector operator in qiskit?

I'm new to qiskit and I want to know how do I define a projector operator in qiskit? Specifically, I have prepared a 3 qubit system, and after applying a whole lot of gates and measuring it in a state ...
54 views

### Test equivalence of circuits exactly on qiskit

I have two circuits that I believe are equivalent. How can one check this on qiskit? Currently, I am executing both circuits and verifying that the counts are close (which they are) but I would like ...
29 views

### Is there a way to generate random circuits in qiskit with only certain allowed gates?

It seems like I can use https://qiskit.org/documentation/stubs/qiskit.circuit.random.random_circuit.html but I would like to control the gates that are allowed. What is an efficient way to make random ...
47 views

### Can Alice and Bob distinguish entangled state coefficients?

Suppose Alice and Bob share the quantum state $\frac{1}{\sqrt 2}(|x\rangle + (-1)^b |y\rangle)$ for some $x\neq y \in \{0,1\}^2$ and $b \in \{0,1\}$. They both do not know $x,y$, and use some ...
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### Is entanglement nonincreasing on average by local operations for all possible ensemble decompositions?

We know for a pure state conversion $|\psi \rangle \rightarrow_\textrm{LOCC} |\phi \rangle$ via local operation and classical communication (LOCC), an entanglement monotone should not increase, that ...
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### Why are there 2 different versions of qiskit installed in anaconda?

When running pip show qiskit-ibmq-provider in the Anaconda Prompt I get the following: ...
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### What is the significance of varying the number of shots while running a circuit in a quantum machine and qasm simulator?

what is the significance of varying the number of shots while running a circuit in a quantum machine and qasm simulator? Does more number of shots give better/accurate result? I am running a simple 2 ...
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### Deriving Expression For QAOA Optimal Trial State Parameters

I am going through the QAOA section in the Qiskit Textbook - QAOA and am stuck in one of the steps. In section 5.2, the method for getting the Optimal Trial State Parameters are discussed. I do not ...