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1500 questions
7
votes
2 answers
Diagrammatic Quantum Reasoning: Proving the loop equation using yanking equations
I'm trying to study the book Picturing Quantum Processes: A First Course in Quantum Theory and Diagrammatic Reasoning and would like some help with Exercise 4.12:
The relevant equations are as follows:
As an aside, I would really appreciate it…
Mahathi Vempati
- 1,731
- 10
- 21
7
votes
1 answer
How to implement a Fredkin gate using Toffoli and CNOTs?
Inspired by a question Toffoli using Fredkin, I tried to do "inverse" task, i.e. to implement Fredkin gate (or controlled swap). In the end I implemented it with three Toffoli gates.
Firstly, I started with swap gate without control qubit which is…
Martin Vesely
- 15,244
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7
votes
4 answers
Nielsen and Chuang, Exercise 6.5: How to simulate oracle for n+1 qubits using one oracle gate for n qubits and one extra qubit?
In Chapter 6 of "Quantum Computation and Quantum Information" textbook by Nielsen and Chuang, Exercise 6.5 p.255:
We have an oracle gate $O$ for $n$ qubit ($2^n=N$ searching items),
and we would like to construct new oracle gate $O'$ for $n+1$…
Alexey Krugovets
- 160
- 10
7
votes
3 answers
Measuring in an arbitrary basis
I'm new to quantum computing, so apologize if my question seems obvious.
Say we have a state $|\Psi\rangle$ and we want to measure it in the computational basis. From what I've been able to understand so far is that, when we make a measure in the…
Skyris
- 167
- 2
- 12
7
votes
1 answer
How good is basic_device_noise_model() simulating the noise in the quantum computer?
Is there any paper or article about the performance of the noise model using basic_device_noise_model()? For example, like the noise model in the code below.
device = IBMQ.get_backend('ibmq_16_melbourne')
properties = device.properties()
noise_model…
Firepanda
- 105
- 5
7
votes
2 answers
Probability estimate in classical Deutsch-Jozsa problem
I have already posed the question on Math SE but I hope that people from QC community can help. I am starting studying QC, but first, I want to understand the classical view of algorithms. So in the following my question:
Here is the description of…
Arnaldo Maccarone
- 173
- 3
7
votes
2 answers
Give an explicit example of a $d = 4$ SIC-POVM
For $q=e^{2 \pi i/3}$, the set of $d^2$ vectors ($d=3$)
\begin{equation}
\left(
\begin{array}{ccc}
0 & 1 & -1 \\
0 & 1 & -q \\
0 & 1 & -q^2 \\
-1 & 0 & 1 \\
-q & 0 & 1 \\
-q^2 & 0 & 1 \\
1 & -1 & 0 \\
1 & -q & 0 \\
1 & -q^2 & 0…
Paul B. Slater
- 957
- 4
- 10
7
votes
3 answers
Pennylane and Qiskit for quantum machine learning
I'm interested in quantum computing, specifically in “quantum machine learning” (QML). I'm going to start my masters program in computer science and have previous experience in classical machine learning. I'd like to learn quantum mechanics…
Carlos Alfredo Vergara Rojas
- 341
- 2
- 10
7
votes
3 answers
Why is the order reversed on measurement?
Why is the order reversed on measurement?
from qiskit import(
QuantumCircuit,
execute,
Aer)
from qiskit.visualization import plot_histogram
# Use Aer's qasm_simulator
simulator = Aer.get_backend('qasm_simulator')
# Create a Quantum Circuit…
Yushan Lu
- 73
- 5
7
votes
1 answer
Can superdense coding be made more efficient?
Superdense encoding allows us to transmit the information of two classical bits using a single qubit with a pre-shared Bell state qubit pair. We can duplicate the construct to transmit $2n$ classical bits using $n$ qubits. My question is: can we do…
czwang
- 949
- 1
- 6
- 17
7
votes
2 answers
Are three POVM measurements on a single qubit physically realizable?
In Nielsen and Chuang Quantum Computation and Quantum Information book section 2.2.6, a POVM of three elements are used to measure a single qubit in order to know for sure whether the state is $|0\rangle$ or $|+\rangle$ if the first two measurement…
czwang
- 949
- 1
- 6
- 17
7
votes
3 answers
How can infinite information be theoretically encoded or stored in a single qubit?
I've just gotten started with Nielsen and Chuang's text, and I'm a little stuck. They mention that theoretically, it would be possible to store an infinite amount of information in the state of a single qubit. I'm not sure I completely comprehend…
agiri
- 484
- 3
- 9
7
votes
2 answers
Significance of the term "diffusion" in Grover's diffusion operator
In the context of Grover's algorithm, the diffusion operator is defined as $U_s = 2|s\rangle \langle s| - I$ with $|s\rangle\equiv |+\rangle^{\otimes n}$. What is the significance of the term "diffusion"? Does it refer to some physical phenomena?
Sanchayan Dutta
- 17,945
- 8
- 50
- 112
7
votes
1 answer
Why does Google's quantum processor outperform IBM's?
I understand that both have 53 qubit devices, yet it is Google that has demonstrated quantum supremacy (although IBM refutes this!). I'm not sure if this is true but it seems like IBM cannot replicate the quantum circuits and measurements that…
user1936752
- 3,311
- 1
- 9
- 24
7
votes
2 answers
Why does a controlled gate not constitute a measurement?
I have recently listened to a talk on quantum computing and was fascinated to learn about IBM Q Experience. Between the explanations in the User Guide and in Nielsen's book, I came to the following question:
Why does a controlled gate not act as a…
DK2AX
- 173
- 5