# All Questions

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### How can I implement an arbitrary quantum channel in a quantum circuit for real experiments using IBM quantum experience?

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 ...
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### Rotation of multi-body interaction in quantum circuit

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 ...
16 views

### Shifting amplitude from one basis to another with a control qubit

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 ...
22 views

### Qiskit unitary representation seems shifted

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): ...
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### What is Ising Hamiltonian ? What its role in Portfolio Diversification?

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 ...
15 views

### What does it look like to split an EPR pair?

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 ...
30 views

### In the context of Quantum theory of Information, Typical eigenvectors are permutations of basis vectors. Why?

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

### Can't load account on IBM's qiskit

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, ...
23 views

### How qubit phase is build in real hardware?

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

### Repeating Quantum Phase Estimation algorithm

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 ...
37 views

### If one had a verifiable solution to P versus NP problem, how, and why, would one go about submitting it?

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 ...
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### It two unitaries are delta apart in trace norm, then what is the trace norm of outputs states when the same input state is applied to two unitaries?

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 $\rho$ ...
27 views

### Find local state and compute Bloch coordinates, like Quirk

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 ...
31 views

### How to perform operations like sin over Qiskit parameters

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

### How to implement exponentiation of a gate without breaking complexity?

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 ...
24 views

### $\lambda$ parameter for U3 gate in qiskit Bloch sphere visualisation

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 ...
26 views

### Finding minimum with Grover

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 ...
28 views

### Qiskit - Z expectation value from counts?

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 ...
18 views

### Is there quantum error correction code package for python

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 ...
12 views

### How to get the $T1$ specs for the Rigetti's quantum processor (Aspen 7)

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 ...
4 views

### Where does the energy going in a Power Rabi experiment with superconducting circuits?

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 ...
39 views

### Topological quantum computer and two dimensional materials

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 ...
18 views

### Quantum circuit CCX optimization for Grover

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 ...
38 views

### Need some help with Purity calculation

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

### Not sure what do Nielsen and Chuang mean by number of operations

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 ...
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### What does the notation $U(B,\beta) = \prod_{j =1}^n e^{-i \beta \sigma_j^x}$ mean in the context of QAOA?

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 ...
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### How to switch bit in the quantum state?

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 $n = 3$ ...
24 views

### Why Alice and Bob don't get the same result when they measure in the same basis?

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 ...
51 views

After placing the Hadamards on the 2 qubits (both initialized in the $|1\rangle$ state) in the circuit, we are given: $|\psi_{b}\rangle = \frac{1}{2}(|0_{1}0_{2}\rangle -|1_{1}0_{2}\rangle -|0_{1}... 2answers 66 views ### Gate Y returns wrong phase in IBM's circuit composer One can check that, with IBM's circuit composer,$Y$gate acted on$|0\rangle$or on$|1\rangle$returns the same phase of$\pi/2$. Is this a bug? 1answer 63 views ### Real backend for my students? I'd like each of my students to run at least one program (however trivial) on a real quantum computer. They can each sign up for accounts on ibm-q-experience. The question is, which of the backends ... 1answer 29 views ### Why does not ibm-q-experience transpile a circuit always in the same way? When I run a certain circuit (using several qubits, it is not a very simple one) in IBM quantum experience, I find that sometimes it is transpiled in one way and sometimes in another. And the final ... 1answer 42 views ### What does the notation$\sigma_j^z\$ mean for Pauli matrices?

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'...

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