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14 views

Am I doing anything wrong when trying to calculate the expectation value in Qiskit on the real hardware?

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 ...
1
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0answers
9 views

Can a Kraus representation be always an identity to any operator?

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, $\...
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1answer
14 views

Randomness using simple parallel Hadamard circuit

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 ...
0
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0answers
12 views

How to construct quantum circuit to count number of 0-qubits and 1-qubits

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, ...
1
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1answer
59 views

How does the graphical notation used to denote doubly-controlled gates work?

$\qquad$ $\qquad$ 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 ...
2
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0answers
14 views

Computing the expectation values of a Hamiltonian constructed from a cost functions in combinatorial optimization

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 ...
3
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1answer
34 views

Is running a for loop faster on a quantum computer than a classical computer?

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?
1
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1answer
74 views

Can quantum computing help to recover a lost private key?

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.
1
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0answers
16 views

What is the pseudo threshold of a QECC using stabilizer formalism

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 ...
0
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1answer
35 views

Confused regarding explanation of Schumachers compression in N&C

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}\...
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1answer
41 views

What can be inferred about the closeness of reduced qubit states from the closeness of the bipartite quantum state?

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 \...
3
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1answer
48 views

Is the Hilbert-Schmidt probability simply zero that a generic rank-2 two-qubit (“pseudo-pure”) density matrix is separable?

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 ...
1
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2answers
52 views

Is there anything Quantikz can do that Tikz cannot do?

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 ...
-2
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1answer
95 views

Operations needed for successful teleportation

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 ...
1
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3answers
49 views

Can you encode two values in a single qubit state, say its phase and orientation?

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,...
2
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0answers
35 views

Recording Quantum Queries

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 { ...
1
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1answer
45 views

Quantum-Assisted Neural Network Training (Is my design reasonable?)

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 ...
2
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2answers
44 views

Find the Kraus operators of a combined amplitude and phase damping channel

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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2answers
77 views

Nielsen and Chuang: Demonstration of equation 2.12

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 ...
2
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1answer
73 views

How to implement Cx mod N unitary

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 ...
1
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1answer
70 views

Why after transpiling a Qiskit circuit we obtain a different result?

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 ...
0
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1answer
41 views

Feedback on Deutsch-Josza alg. homework prob. in Learning Quantum computation using Qiskit [closed]

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: ...
0
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1answer
62 views

How the simulator work?

Recently I focused on how to simulate in classical computer, and I found Qiskit offers qasmsimulator and statevector simulator. ...
1
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1answer
21 views

Applying a gate to all line qubits without explicitly listing them in Cirq

Say we have a custom gate CG, defined by a unitary matrix U, and line qubits qubits in Cirq. ...
1
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1answer
29 views

Visualizing custom gates 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 ...
2
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1answer
39 views

Calcuate $\langle x | D | y \rangle$ for arbitrary $x,y \in \{0,1\}^n$

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 \...
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2answers
41 views

Are there any resources of lists of attempts at non-probabilistic models of quantum mechanics, with debunking?

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 ...
0
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1answer
29 views

Question regarding part of the proof for the typical subspace theorem

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 ...
1
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1answer
28 views

What is the representative matrix for a measurement in the Bell-state basis?

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 ...
1
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1answer
55 views

What extra functionality is available to an IBM Q Network member over a regular IBM Q Experience user

I've been trying to figure out the extra functionality available to IBM Q Network members that are not available to normal ...
0
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1answer
33 views

How can I represent mixed states in Q#?

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 ...
0
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1answer
38 views

Question About How Qiskit Reset Gate Affects Other Entangled Qubits

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 ...
1
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1answer
74 views

Correct interpretation of a Quantum State

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 ...
4
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1answer
98 views

Energy cost of quantum computation

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 ...
0
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2answers
49 views

Is there a notion of “computational security” in quantum cryptography?

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 ...
2
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1answer
73 views

How to prepare a quantum circuit for $\frac{1}{\sqrt{3}}(|00\rangle+|01\rangle+|10\rangle)$ starting from $|00\rangle$

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 ...
1
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0answers
38 views

Step-by-step passages in calculation

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)(...
4
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2answers
72 views

How to measure the sign of quantum amplitudes

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 ...
2
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1answer
246 views

Quantum Circuit To Compute Any Inner Product

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,...
2
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1answer
117 views

Are the skills learned for a degree in Computer Engineering helpful in learning Quantum Computing? [closed]

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 ...
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0answers
32 views

I'm trying to import random_state from qiskit_textbook.tools but it gives error message [closed]

I am getting this error during import random_state from qiskit_textbook.tools: ...
1
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1answer
36 views

Quantum Error Correcting Codes and Graphs

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 ...
0
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1answer
24 views

Interconnection clarification?

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 ...
3
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1answer
47 views

Grover's Algorithm on a Database with more than 50% matching entries

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 ...
2
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1answer
52 views

How do you embed a POVM matrix in a Unitary?

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. ...
2
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1answer
65 views

Confusion regarding time complexity in the HHL algorithm

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 $\tilde{O}\left(\log (N) s^{2} t_0\right)$. ...
1
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2answers
61 views

How can a half-wave plate affect the position qubit and not the polarization qubit of a photon?

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). ...
4
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3answers
78 views

Can you transform a quantum program into an arrangement of slits?

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 ...
2
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0answers
46 views

Coherent Information and Entanglement Breaking channels

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 ...

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