All Questions

Let's suppose I have a quantum channel given in the Kraus decomposition $T(\rho) = \sum_{i} K_i \rho K_i^{\dagger} $ is there any way to put explicitly these $K_i$ in IBM quantum experience (QE) to ...

In quantum circuit, how do you implement the rotation of multi-body interaction, such as $e^{-i\theta\sigma_z^1\sigma_z^2\sigma_z^3}$? I already know the case of less than two-body interaction, but I ...

I was reading a forum where people were talking about a proposed quantum algorithm that solves an NP-complete problem in polynomial time. The algorithm appears to have flaws (after all, none of you ...

I have implemented a simple CNOT gate using qiskit I was expecting a the result the matrix as in the following image (extracted from wikipedia): ...

I am asking this question with reference to this https://github.com/Qiskit/qiskit-iqx-tutorials/blob/master/qiskit/advanced/aqua/finance/optimization/portfolio_diversification.ipynb Happy to know new ...

I am reading Quantum Computation and Quantum Information by Michael A. Nielsen & Isaac L. Chuang, and I am confused about a concept presented in Section 1.3.7: Quantum Teleportation. The book ...

Why is this so? Can someone please give me detailed steps with an explanation?

The command load account keeps giving the warning that it can't find a QConfig file. A search for the error message brings me to an answered question. However, this solution also doesn't work, ...

How qubit phase is build in real hardware? On IBM Quantum, D-Wave, etc?

In the Quantum Recommendation Systems paper, the authors use the Quantum Phase Estimation algorithm in a way that is slightly different from what I've seen so far. This is how it is described: The ...

Asking for a friend. The exclusivity/elitism of the field (and the dominance-human hierarchy), as well as the outcomes of "exploitation of "discoveries" throughout history have friend leaning away ...

On Wikipedia, one can read the following about Quantum Phase Estimation: the algorithm estimates the value of $\theta$ with high probability within additive error $\varepsilon$, using $O(1/\...

There was a similar question asked here, but I feel like mine is even more basic. What's the easiest way to implement a circuit $U$ corresponding to matrix multiplication modulo 2? $$ |x_1x_2x_3\...

I have been reading the book by Michael A Nielsen and Isaac Chuang and came across the principle of deferred measurement. They showed using this principle how the circuit for quantum teleportation can ...

I've read C-NOT gate entangles qubits, but is it only for C-NOT or any arbitrary CU gate (apart from the likes if CI) entangles qubits?

I have installed qiskit through my terminal using pip3 install qiskit. But when I try to import all from it in my coding software, it returns a M...

I made a simple circuit that we can see. In my view, $|00000\rangle$ should appear in one result, but I didn't see it. why?

In last year‘s conference "Quantum For Business 2019" Iordanis Kerenidis gave a nice talk about quantum machine learning. At about time 27:10 he mentions a "Quantum Data loader" as an alternativ for ...

I recently had an assignment where the question is based on the assumption that we can write any pure state qubit $|\phi \rangle$ as: $$|\phi \rangle = \gamma |\psi\rangle + \delta |\psi^\perp ...

One of the main application of VQE is its application to find the approximation to the ground state energy (smallest eigenvalue) for a particular molecule through an iterative method. To be able to ...

In the paper Valley qubit in Gated MoS$_2$ monolayer quantum dot, a description of how a $NOT$ gate would be performed on a qubit in the described device is given. The authors say that in the ...

In order to build a custom noise model in Qiskit Aer, I requested the error parameters from different backends and got 3 (9) parameters for each single-qubit (two-qubit) gate as output. However, I ...

I have a question concerning the placement of quantum circuits on Google devices. Consider the following code: ...

In the paper Quantum Observables for continuous control of the Quantum Approximate Optimization Algorithm via Reinforcement Learning, an Hamiltonian is defined in order to solve the MAXCUT problem : $...

I have the following simple quantum circuit: This outputs are 00 and 11 for the two qubits. Using matrices, I have applied the H gate to the first qubit (ket 0): $\frac{1}{\sqrt{2}}\begin{pmatrix}1&...

In HHL algorithm, for subroutine involving controlled rotation, after applying $R_y(\theta)$, where $\theta=\frac{2C}{\lambda}$ to the ancilla, the state changes to $\sqrt{1-\frac{C^2}{\lambda^2}}|0\...

Suppose we are given two unitary matrices $U$ and $V$, with the following guarantee, $$||U - V||_1 \geqslant \delta$$ for some $\delta \geqslant 0$. We apply an input density state $\rho$ ...

In a multi-qubit system I can find the amplitudes of a state and compute probabilities, $\theta$, and $\varphi$. This falls out from simulation with simple numpy arrays. For example, after application ...

I want to create a parameter dependent gate in qiskit and I need to compute some complex operations as sympy.atan2 or sympy.sin ...

In the application of QFT for quantum phase estimation (QPE) of a unitary $\mathbf{U}$, one has to perform successive controlled operations using powers of $\mathbf{U}$. In order not to break the ...

It is easy to see how $\theta$ (rotation from the positive z-axis) and $\varphi$ (rotation from the positive z-axis) affect the initial state of the qubit when looking at the Bloch sphere but I have ...

I am a beginner in quantum computing. I have already computed the sat quantum solver with Grover search and then, I would like to compute the "minimum search" of Dür and Hoyer. My question is: Is it ...

For a given state $|\psi\rangle$, how would I work out $\langle\psi|Z|\psi\rangle$ ? If I run a quantum circuit and get the counts dictionary on qiskit, I get observables in the Z basis. For n=1 ...

I'm working on the development of a new quantum error correction protocol that tries to maximize the coherence of the qubit. Is there a package for python, similar to qutip, that could help me in this ...

I am trying to find the $T1$ coherence time for different qubits of Rigetti's quantum processor (Aspen 7) using Python. I tried using Specs() but encountered an ...

When performing a Power-Rabi experiment, e.g in superconducting circuits, we are playing a pulse to a qubit and then reading out its state by playing another pulse to a dispersively-coupled readout ...

Recently I read thread on topological quantum computers. If I understood correctly, gates in such computers are based on "effects" in two dimensional spaces. Since our space is three dimensional, such ...

I am working on a circuit for a Grover problem and during that I am trying to minimize the used QuBits. The problem is shown in the attached image. In this case the circuit is more or less efficient ...

maybe you could help me a little about my calculation of a quantum pure state with purification. I have this density matrix: \begin{equation} \rho= \begin{pmatrix} 0.4489 & 0.2304 & 0.2162 &...

I am reading Nielsen and Chuang's "Quantum Computation and Quantum Information". One important concept about algorithms is how the number of operations scales with the length of the input. I realized ...

In the article Quantum Observables for continuous control of the Quantum Approximate Optimization Algorithm via Reinforcement Learning, the following notation is used to describe an Unitary operation ...

I'm given with a Hamiltonian, $H=H_1+H_2$, where $H_1=\sigma_x\otimes\sigma_z$ and $H_2=\sigma_y\otimes\sigma_y$, and want to built a circuit which will implement $e^{-iHt},t=\pi/6$. We see that as $\...

In Google's Quantum Supremacy experiment, they use $f_{sim}$(fermionic-simulation) gates with $\theta=90°$ and $\phi=30°$ as their two-qubit gates. What if we use $\theta=45°$ for the two-qubit $f_{...

I want to transform binary representation from one to other. Here, I have 2 registers one act as control register and another is target register with the same number of qubits $n$. Consider $n = 3$ ...

I'm simulating the BB84 protocol using simulaqron. My problem is that when Alice and Bob measure in the same basis, they don't get the same result. How can I fix this error? . BB84.py ...

After placing the Hadamards on the 2 qubits (both initialized in the $|1\rangle$ state) in the circuit, we are given: $ |\psi_{b}\rangle = \frac{1}{2}(|0_{1}0_{2}\rangle -|1_{1}0_{2}\rangle -|0_{1}...

One can check that, with IBM's circuit composer, $Y$ gate acted on $|0\rangle$ or on $|1\rangle$ returns the same phase of $\pi/2$. Is this a bug?

I'd like each of my students to run at least one program (however trivial) on a real quantum computer. They can each sign up for accounts on ibm-q-experience. The question is, which of the backends ...

When I run a certain circuit (using several qubits, it is not a very simple one) in IBM quantum experience, I find that sometimes it is transpiled in one way and sometimes in another. And the final ...

In multiples papers or online article on the QAOA algorithm (such as this one), I found notation for the Hamiltonian similar to this one : $$ \sum_{ij} \frac{1}{2} (I-\sigma_i^z \sigma_j^z)$$ I don'...