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1500 questions
7
votes
1 answer
Can a Toffoli gate be implemented using Fredkin gates?
Even though this seems to be a much asked basic question, I couldn't find a reputed answer to this:
Implement a 3-qubit Toffoli gate using 3-qubit Fredkin gates.
The best I could do was using 4 gates to give
Can we use less than 4 gates?
In the…
lineage
- 173
- 5
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
2 answers
How to transform e.g., a 4 by 4 unitary matrix into a quantum circuit
I am new to Quantum Computing. I would really appreciate if some one could offer me some ideas, suggestions and/or useful references to solve the following problem about realizing an arbitrary operator by a quantum circuit.
If I start with a general…
Marxmas
- 107
- 1
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7
votes
1 answer
How to prepare Unitary Coupled Cluster ansatz for VQE in a circuit?
I have read the following paper by Dumitrescu et al.
To make a Unitary Coupled Cluster (UCC) ansatz, one prepares with the following equation.
$$
| \psi_{\rm{UCC}} \rangle = U(\theta)|\mathrm{HF}\rangle
$$
Here, $U(\theta) = \exp[ T(\theta) -…
Ashy
- 375
- 1
- 6
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
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
- 849
- 1
- 6
- 16
7
votes
1 answer
Why is the probability vector of a uniformly random state $\sum_i\alpha_i|i\rangle$ uniformly random only if $\alpha_i\in\mathbb C$?
In these lecture notes by Scott Aaronson, the author states the following (towards the end of the document, just before the Linearity section):
There's actually another phenomenon with the same "Goldilocks" flavor, which was observed by Bill…
glS
- 24,708
- 5
- 34
- 108
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
- 17,497
- 7
- 48
- 110
7
votes
1 answer
How to selectively apply noise in Qiskit simulations?
In Qiskit it is possible to specify noise models to apply to simulations. This allows noise to be defined for certain operations, like measurement or each type of gate.
Is it also possible to change the noise for different parts of the circuit. Such…
James Wootton
- 11,272
- 1
- 31
- 72
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
- 2,859
- 1
- 8
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7
votes
3 answers
Is quantum complexity basis-invariant?
Quantum computing refers (occasionally implicitly) to a "computational basis".
Some texts posit that such a basis may arise from a physically "natural" choice.
Both mathematics and physics require meaningful notions to be invariant under a change of…
Martin Ziegler
- 73
- 4