Most Popular
1500 questions
8
votes
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
- 81
- 1
- 4
8
votes
1 answer
Is the Clifford group finite?
For any fixed $n$, how do we prove that the $n$-qubit Clifford group (subgroup of $ U(2^n) $ generated by Hadmard gates, phase-shift gates and CNOT gates) is finte or not? I know that for the single qubit case, where only H gate and S gate are…
Conn-CaoYK
- 171
- 1
- 7
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
- 333
- 1
- 6
8
votes
2 answers
Making custom gate in Qiskit?
I have been trying to make a gate in qiskit in terms of the basic gates, but I keep on getting an error when I apply it to a circuit.
This is my gate:
class LGate(Gate):
def __init__(self, label=None):
super().__init__('l', 1, [],…
Tech333
- 101
- 1
- 2
8
votes
3 answers
What does the adjoint of a channel represent physically?
Given a quantum channel (CPTP map) $\Phi:\mathcal X\to\mathcal Y$, its adjoint is the CPTP map $\Phi^\dagger:\mathcal Y\to\mathcal X$ such that, for all $X\in\mathcal X$ and $Y\in\mathcal Y$,
$$\langle Y,\Phi(X)\rangle= \langle…
glS
- 27,510
- 7
- 37
- 125
8
votes
2 answers
Why attenuator and not filters for QC driving line
In all the cold quantum computer designs (superconducting qubits, spin qubits) attenuators are put on the driving lines. Their role is to kill the noise spectral density that comes from higher temperature stages, such as the Johnson-Nyquist noise.…
Marco Fellous-Asiani
- 2,220
- 2
- 15
- 42
8
votes
3 answers
How to implement a while loop in a quantum computer?
How can a while loop be implemented in a quantum computer?
If quantum computing consists of :
preparing a state
applying a unitary operator
measuring,
then it seems like it's not possible to wait for an indefinite amount of time before…
Nichola
- 411
- 2
- 9
8
votes
3 answers
Compiling a classical function to a quantum circuit in practice
It can be shown that any classical function $f$ can be implemented by a quantum circuit $Q_f$, so that
$$
\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
- 81
- 2
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
- 662
- 7
- 13
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
- 183
- 4
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
- 255
- 2
- 7
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
- 7
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 satisfies $a^2 + b^2 = 1$. 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
- 207
- 1
- 5
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
- 143
- 5
8
votes
1 answer
How to construct Deutsch's gate or $\pi/8$ rotations using Toffoli+Hadamard?
It is known that Toffoli and Hadamard are Quantum Universal.
My question is - how to construct (an approximation of) the Deutsch's gate or the $\pi/8$ rotation using Toffoli + Hadamard?
I've seen several implementations of the Toffoli gate using…
GWB
- 211
- 1
- 2