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1500 questions
8
votes
2 answers
How to compute the measurement probability in swap test?
The figure of a circuit and the state are as follows.
The final state before the measurement is…
karry
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8
votes
1 answer
How to create an arbitrary state in QISKit for a local_qasm_simulator?
I would like to play with a quantum circuit local_qasm_simulator in QISKit, but I do not want to implement a separate quantum circuit that would prepare an initial state.
The way I do it now is by falling back to NumPy. Specifically, first, I…
Alexander Pozdneev
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8
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1 answer
Qiskit - difference between qasm_simulator and statevector_simulator in terms of memory and speed?
I'm trying to profile qiskit backends and I use randomized_benchmarking provided by qiskit.ignis.
Initially I ran a circuit with 20 qubits 100 length on statevector_simulator, which takes around 180s and qubits can go up to 32 and then it runs out…
izumi
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8
votes
1 answer
Circuit for VQE Expectation Value Finding
I'm looking into the circuit for the VQE, but am stumped at how we can identify the expectation value of the Pauli series. Essentially, how do we find:
$$ \langle \psi | H_i | \psi \rangle $$
Given $H_i$ can be decomposed into Paulis?
The first…
C. Kang
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8
votes
3 answers
What are the differences between the IBM machines?
I'm quite new to this field, and have started sending jobs to IBM's quantum computers. I have access to around 11 locations. I can see that these have different numbers of qubits within them, and then different layouts of them as well.
I am trying…
Andrew
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8
votes
3 answers
What does quantum gate fidelity mean?
The formal definition states that it's the distance between two quantum states. What does that mean experimentally? Does distance here mean the distance between two states on the Bloch Sphere? I am a little confused about the meaning of gate…
Maxx
- 161
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8
votes
2 answers
Why attenuator and not filters for QC driving line
In all the cold quantum computer designs (superconducting qubits, spin qubits) attenuators are put on the driving lines. Their role is to kill the noise spectral density that comes from higher temperature stages, such as the Johnson-Nyquist noise.…
Marco Fellous-Asiani
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8
votes
3 answers
Is the tensor product of two states commutative?
I'm reading "Quantum Computing Expained" of David McMahon, and encountered a confusing concept.
In the beginning of Chapter 4, author described the tensor product as below:
To construct a basis for the larger Hilbert space, we simply form…
akawarren
- 81
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8
votes
3 answers
Compiling a classical function to a quantum circuit in practice
It can be shown that any classical function $f$ can be implemented by a quantum circuit $Q_f$, so that
$$
\sum_{x}|x,0^k\rangle \xrightarrow{\mathit{Q_f}} \sum_{x}|x,f(x)\rangle
$$
where $f$ has $k$ output bits, and ingnoring normalization. I have…
kgi
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8
votes
2 answers
There was an error in the circuit!. Error = 'QISkit Time Out'
I've got the following quantum code using QISKit (based on hello_quantum.py):
import sys, os
from qiskit import QuantumProgram, QISKitError, RegisterSizeError
# Create a QuantumProgram object instance.
Q_program = QuantumProgram()
try:
import…
kenorb
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8
votes
1 answer
What are the thermodynamic limits of Shor's algorithm
The asymptotic time complexity of Grover's algorithm is the square root of the time of a brute force algorithm. However, according to Perlner and Liu, the thermodynamic behavior (theoretical minimum on energy consumption) is asymptotically the same…
Nic
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8
votes
1 answer
New algorithm for faster QC simulation by IBM
This new algorithm for QC calculation was introduced recently (2017 4Q) by IBM/ Pednault et al. to great fanfare. The paper seems more couched in the language of physics.
Are there any basic overview/analyses of this by computer scientists about…
vzn
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8
votes
1 answer
What are the implications of Bremermann's limit for quantum computing?
The title says most of it: What are the implications of Bremermann's limit for quantum computing?
The Wikipedia page says that the limit applies to any self-contained system, but in the last few lines they also claim that "access to quantum memory…
wythagoras
- 181
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8
votes
2 answers
Is it right to think of superposition as just angle?
Based on my current understanding, a qubit is represented as a vector $(a, b)$ which satisfy $a^2 + b^2 = 1$. Classical bit one can be represented as $(0, 1)$ and bit zero can be represented as $(1, 0)$.
And then we can have things that cannot be…
Wong Jia Hau
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8
votes
1 answer
Will two entangled qubits be affected by gravity?
Will two entangled qubits be affected by gravity? I mean if one is near blackhole's horizon and other is on earth will the effect of relativity be experienced on the measurement? will there be any delay or error in measurement?
varun palakodeti
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