All Questions

I am trying to use the method of calculating the expectation values of Pauli operators in Qiskit which I found here. However, the results obtained via IBMQ sampling differ significantly from the exact ...

In the textbook “Quantum Computation and Quantum Information” by Nielsen and Chuang, it is stated that there exists a set of unitaries $U_i$ and a probability distribution $p_i$ for any matrix A, $\...

I've recently tried to build a Random generator using 5 hadamard gates (shown as U2 below) measured to 5 classical bits in parallel as shown in the circuit image. I've executed this circuit for 8192 ...

Suppose we have a 3-qubit input; each bit is either 0 or 1. How to decide if there are more 1's than 0's? (Only 1 extra qubit and single/double qubit gates can be used; you cannot use toffoli gates, ...

$\qquad$ $\qquad$ What is the difference between solid and hollow? How to express the corresponding matrix of these figures? In addition, if they are not adjacent, what should be done in the middle of ...

One of the main steps in Hybrid Quantum algorithms for solving Combinatorial Optimization problems is the calculation of the expected value of a hermitian operator $H = \sum{H_i}$ (where $H_i$ are ...

Curious to understand if I run for loop within a quantum algorithm, and lets say I want the quantum algorithm to run in classical run time of O(1). Can this be done?

I lost a private key for an ethereum wallet. While seeking for information I found out that only quantum computers can decrypt a public key. Is this really a possibility? Thanks in advance.

Can someone explain what is the threshold and the pseudo threshold of a Quantum Error Correction Code , for instance the 9-qubit code. I'm familiar with quantum information and quantum circuit and ...

On page 547 of N&C, for $|\psi_{0}\rangle=|0\rangle$ and $|\psi_{1}\rangle=(|0\rangle+|1\rangle)/\sqrt{2}$ and for $|\tilde{0}\rangle=\cos(\pi/8)|0\rangle+\sin(\pi/8)|1\rangle$ and $|\tilde{1}\...

Given a qubit state $|\psi\rangle \in \mathcal{H}$, and two bipartite general mixed states $\rho$ and $\sigma$, such that, $$\langle \psi|\otimes \langle \psi|\rho - \sigma |\psi\rangle \otimes |\psi \...

The multifacted evidence is very compelling--although not yet presented in a formal proof--that the Hilbert-Schmidt probability that a generic (full rank/rank-4) two-qubit density matrix is separable ...

I am learning how to draw quantum circuits. I was checking the options available and I could see that Tikz and Quantikz are suitable for making circuits diagrams but I want to know if there are some ...

I am trying to make a circuit to teleport a single qubit using three-particle entangled. I have come down to the following case involving a total of $4$ qubits. I need to teleport the first qubit to ...

I had an interesting talk with someone who said that we can use a single qubit to encode two different values. We encode the first value in its orientation (up/down) of particle/wave (electron, photon,...

Question is about techniques from this paper. Essentially the paper provides a way to record what queries were asked to a quantum-accessible oracle. We have the oracles: \begin{aligned} &\text { ...

I'm a college student with a slight interest in quantum mechanics. I think I have a decent understanding of the Copenhagen and Many Worlds interpretations of quantum mechanics, and was considering how ...

I am going through the paper Surface code with decoherence: An analysis of three superconducting architectures and I have a doubt about how the authors get what they refer to as the combined channel ...

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First, I apologize if something is poorly written but English is not my first language. Reproduced from Nielsen & Chuang's Quantum Computation and Quantum Information (10th Anniversary Edition) in ...

The following links provides circuts for $a\in\{2,7,8,11,13\}$ and $N=15$: https://qiskit.org/textbook/ch-algorithms/shor.html#3.-Qiskit-Implementation https://arxiv.org/abs/1202.6614v3. I am ...

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 ...

In Learning Quantum Computation using Qiskit chapter 3.4 I encountered the Deutsch-Josza Algorithm. At the end of the chapter I was presented with a homework problem where the code: ...

Recently I focused on how to simulate in classical computer, and I found Qiskit offers qasmsimulator and statevector simulator. ...

Say we have a custom gate CG, defined by a unitary matrix U, and line qubits qubits in Cirq. ...

I'm trying to visualize a custom gate in Cirq. I have through this page, which briefly mentions how to create custom gates in Cirq. However, I'm getting errors when trying to visualize it. My current ...

We are considering Grover's algorithm with a search space of size $2^n$ for an arbitrary integer $n$ for arbitrary $n$, and a unique marked element $x_0$. Question: Calculate $\langle x | D | y \...

For example, some introductory resource I was reading years ago (forget which one) brought up such an attempt: imagine if a qbit wasn't a complex state vector which collapses probabilistically on ...

Part three (going by N&C page 544) states that $$tr(S(n)\rho^{\otimes n})=tr(S(n)\rho^{\otimes n}P(n,\epsilon))+tr(S(n)\rho^{\otimes n}(I-P(n,\epsilon))).$$ Now I understand how the term on the ...

I have a few questions about measurement in Bell-state basis. In particular, if $Z = \begin{bmatrix} 1 & 0\\ 0 & -1 \end{bmatrix}$ is for a measurement on the computational basis, then what ...

I've been trying to figure out the extra functionality available to IBM Q Network members that are not available to normal ...

I have a mixed state with a density matrices corresponding to $\rho=\sum_0^{2^n-1}p_i|i\rangle\langle i|$. How would i represent this in Q#? How would I go about applying Unitary Operations $U$ on ...

I am trying to understand how the reset gate in Qiskit affects qubits its entangled with. Consider the following circuit with qubits $q_0$ and $q_1$: Where circuit240 takes $|0\rangle$ to $a|0\rangle ...

If a quantum system is described to be only in Quantum states $s_1$ and $s_2$ (described by computational basis $\vert {0} \rangle$ and $\vert {1}\rangle$) or a combination of both (for a qubit system ...

A quantum computer can be modeled as a single unitary transition of a (large) effective quantum state to another. In order to get errors under control, quantum error correction is assumed. A logical ...

In classical cryptography, security proofs are often based on the (assumed) computational hardness of some mathematical problem. Using the principles of quantum mechanics might provide means to design ...

How do I prepare a quantum circuit for $\frac{1}{\sqrt{3}}(|00\rangle+|01\rangle+|10\rangle)$ state starting from the $|00\rangle$ state? I have no clue how to do it. I tried with controlled Hadamard ...

I would like to better understand some passages in a paper (Appendix A): Properties of Tensor Product Bilinearity: $A\otimes(B+ C) = A \otimes B + A \otimes C $ Mixed-product property: $(A\otimes B)(...

I have a quantum state on $ n $ qubits ($ 2^n $ amplitudes) for which I know the amplitudes are real numbers. I want to take the state out as a vector. I can estimate the magnitude of the amplitudes ...

I'm currently reading the paper Classification with Quantum Neural Networks on Near Term Processors It shows a method to determine the following quantity: Where U is a unitary operator acting on $|z,...

Next year, I will be a senior Computer Engineering student. Saying that, I have studied computer organization, electrical circuits, electronics and data structures. Our university provides an ...

I am getting this error during import random_state from qiskit_textbook.tools: ...

Couple of weeks ago I asked this question on theory CS but I didn't get an answer. So trying it here. I was reading combinatorial approach towards quantum correction. A lot of work in this is on ...

I just want to clear what seems to be a bit confusing to me with quantum gates and their corresponding output. below are 3 scenarios implementing two hadamard gates two hadamard gates on one qubit ...

The Setup for Grover's Algorithm is the following: Given an oracle $f_O^{\pm}$ representing a Query on a Database with total $N$ entries $N$ of which $k$ are matching. Grover's Algorithm is used to ...

In QuantumKatas Measurement Task 2.3 - Peres-Wooter's Game, we are given 3 states A,B and C. We construct a POVM of these states. But how do we convert that POVM into a Unitary that we can apply. ...

In the paper of HHL algorithm (Quantum algorithm for linear systems of equations), the time complexity of simulating $e^{i A t}$ for a hermitian matrix A is $\tilde{O}\left(\log (N) s^{2} t_0\right)$. ...

I recently was watching these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits). ...

Is it possible (in theory) to convert any problem that can be solved on a quantum computer into an arrangement of slits carved into a piece of metal foil, and then to run the program by shining light ...

The book by John Watrous, "The Theory of Quantum Information" is an exciting read for anyone wanting to research quantum information theory. The following question presumes some background ...