Questions tagged [noise]
For questions about different types of noise a quantum computer (or qubits) may experience; how this affects the outcome of the computation; how to reduce a specific type of noise on a specific implementation of quantum computer; or how to simulate noise.
227 questions
26
votes
4
answers
2k
views
Is error correction necessary?
Why do you need error correction? My understanding is that error correction removes errors from noise, but noise should average itself out. To make clear what I'm asking, why can't you, instead of ...
- 3,469
24
votes
3
answers
1k
views
Which quantum error correction code has the highest threshold (as proven at the time of writing this)?
Which quantum error correction code currently holds the record in terms of the highest threshold for fault-tolerance? I know that the surface code is pretty good ($\approx10^{-2}$?), but finding exact ...
- 2,457
18
votes
3
answers
819
views
What exactly is meant by "noise" in the following context?
The strengthened version of the Church-Turing thesis states that:
Any algorithmic process can be simulated efficiently using a Turing machine.
Now, on page 5 (chapter 1), the book Quantum ...
- 17.8k
15
votes
1
answer
480
views
How does approximating gates via universal gates scale with the length of the computation?
I understand that there is a constructive proof that arbitrary gates can be approximated by a finite universal gate set, which is the Solovay–Kitaev Theorem.
However, the approximation introduces an ...
- 2,457
9
votes
2
answers
736
views
How do quantum computers prevent "quantum noise"?
On the Wikipedia page for Shor's algorithm, it is stated that Shor's algorithm is not currently feasible to use to factor RSA-sized numbers, because a quantum computer has not been built with enough ...
- 193
9
votes
1
answer
2k
views
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 ...
- 11.5k
8
votes
4
answers
1k
views
Simulating a quantum circuit with decoherence and noise
Based on the answers given here and here, it is pretty clear that an arbitrary quantum circuit can be simulated with matrix algebra. The difficulty is that this assume perfect fidelity. I am unsure ...
- 701
8
votes
2
answers
679
views
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 ...
- 1,952
8
votes
1
answer
2k
views
Depolarizing channel implementation on IBM Q
Given a single qubit in the computational basis, $|\psi\rangle =\alpha |0\rangle + \beta|1\rangle$, the density matrix is $\rho=|\psi\rangle\langle\psi|=\begin{pmatrix} \alpha^2 & \alpha \beta^*\\
...
- 495
7
votes
1
answer
1k
views
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.
...
- 105
7
votes
1
answer
500
views
Degradable channels and their quantum capacity
Note: I'm reposting this question as it was deleted by the original author, so that we do not lose out on the existing answer there, by Prof. Watrous. Further answers are obviously welcome.
I have ...
- 17.8k
7
votes
2
answers
627
views
Is it true that observing a quantum state will end the superposition of states? How can I not observe?
I have no background in quantum physics, and no understanding of most formulas used in this context. I'm not looking for an in depth answer, i'd just like to vaguely understand the concept.
The way i ...
- 173
7
votes
1
answer
913
views
Quantum teleportation with "noisy" entangled state
This is actually an exercise from Preskill (chapter 4, new version 4.4). So they are asking about the fidelity of teleporting a random pure quantum state from Bob to Alice, who both have one qubit of ...
- 555
7
votes
1
answer
339
views
How are Rigetti and IBM QX device parameters related to Kraus operators?
Rigetti reports the following parameters: (https://www.rigetti.com/qpu)
T1, T2* times
1-qubit gate fidelity (F1q)
2-qubit gate fidelity (F2q) and,
read-out fidelity (Fro)
IBM QX reports the ...
- 429
7
votes
2
answers
323
views
Derive phase damping quantum operation
I am reading about the phase damping quantum operation on page 384 of Nielsen & Chuang's Quantum Computation and Quantum Information (10th Anniversary Edition).
Nielsen & Chuang derived the ...
- 171
7
votes
1
answer
158
views
Threshold and practical requirements for initial state preparation?
At the beginning of a quantum computational process we generally want to start in a perfectly known initial state, and evolve from there. This cannot be done perfectly, for fundamental reasons, but I ...
- 3,887
7
votes
2
answers
313
views
Does Barkhausen noise affect the measurement of magnetic particle based qubits?
Q1: I've tried to find out if Barkhausen noise affects the measurement of spin-wave excitations in magnetic particle material based qubits.
I prefer implementations such as those described in "...
- 2,319
7
votes
0
answers
354
views
How to make qubits more stable towards noise? [closed]
In this paper and this paper, the "Noise Stability of Qubits" (the stability of qubits to external noise) has been discussed. In the first one, Gil Kalai states that it is difficult to ...
- 179
6
votes
2
answers
945
views
Explicit form for composition of Choi representation quantum channels
Let $|\Omega \rangle$ be the maximally entangled state over a bipartite system whose parts are each dimension $d$, i.e.
$$
| \Omega \rangle \equiv \sum_i^{d}| ii \rangle
$$
Then one way of writing ...
- 7,646
6
votes
1
answer
2k
views
Qubit dephasing times
The dephasing time (also known as decoherence time in the literature), $T_2$, speaks about the timescale in which qubits experience dephasing effects. This relates with the decay of the off-diagonal ...
6
votes
2
answers
240
views
Proven quantum advantage (in the algorithmic sense) without error correction (for specific algo, or noise models)
I would like to know if there are some specific class of quantum algorithms, under some hypotheses about the noise model behind the quantum gates for which we know that there is an exponential ...
- 1,952
5
votes
2
answers
711
views
Are operators unitary on a real quantum computer?
The question is more from the physical side of quantum computers. Can we say that operators are unitary or due to the NISQ nature, the operator (impact on particles) in reality deviates from this ...
5
votes
2
answers
1k
views
What is the clear definition of coherent versus incoherent errors?
The noise types in quantum computing are pivotal topics frequently discussed in academic papers.
Could you provide a clear definition of coherent versus incoherent errors? Additionally, I'm keen to ...
- 63
5
votes
2
answers
1k
views
Determining whether there exists an equivalent set of unitary Kraus operators
I have a CPTP quantum channel $\mathcal{E}$ that I've characterized by an operator sum representation $\{E_i\}$ for $i=1, \dots, m$ which acts on an input state like
$$
\mathcal{E}(\rho) = \sum_{i=1}^...
- 7,646
5
votes
3
answers
998
views
How are eavesdroppers detected when using BB84 in the presence of noise?
I would like to expand upon this question: What is the probability of detecting Eve's tampering, in BB84?
Let's say that when the receiver (colloquially referred to as Bob) receives a qubit and ...
- 1,459
5
votes
1
answer
647
views
Incorporating idling errors while using stim
Is there a smart way to incorporate idling errors for a quantum error correction code using the open-source tool stim (preferably using the tableau simulator)? I have perused the code repository, as ...
- 246
5
votes
1
answer
692
views
How can noise on a device be simulated using measured noise parameters?
The real devices used as backends for Qiskit have calibration data that quantifies errors ($T_1$ and $T_2$, gate fidelities, etc). This can be accessed by, for example
...
- 11.5k
5
votes
1
answer
758
views
How to not optimize the quantum gates in a qiskit circuit when running it in the real device?
I have been trying to run two circuits in the ibmq_london device, the one resulting of applying one X gate on qubit $0$ and the one that applies two X gates. I know that applying two X gates is the ...
- 389
5
votes
1
answer
550
views
Why does the bit flip channel produce a uniform contraction of $1-2p$?
Studying the bit flip channel using the Nielsen & Chuang's.
And ran into the picture with the caption stating $yz$ plane is uniformly contracted by a factor of $1-2p$. I don't quite understand how ...
- 1,161
5
votes
1
answer
356
views
Qudits in NISQ Devices: Benefits Beyond Dimensional Advantages?
It's clear from foundational research that qudits can provide an enhanced control of the Hilbert space over qubits, and I've encountered references that highlight improved robustness and noise ...
- 867
5
votes
1
answer
157
views
How's quantum noise and fault-tolerance related to symplectic geometry and geometric quantization?
Gil Kalai often speaks of the apparent connection between symplectic geometry, geometric quantization, and quantum noise. He is known to describe one of his focus areas as:
(...) properties and ...
- 17.8k
5
votes
1
answer
452
views
What are the physical reasons behind noise/errors in quantum computers?
We know that the current quantum computers are noisy/error-prone. They are susceptible to gate errors (single qubit and multi-qubit), decoherence (relaxation and dephasing), readout error, etc. I want ...
- 429
5
votes
0
answers
662
views
Add noise_model when using 'ibmq_qasm_simulator' backend and provider.runtime.run() function
I am trying to test some qiskit code that employs readout-error mitigation using the ibmq_qasm_simulator backend and Qiskit Runtime. I am getting the backend as ...
- 51
4
votes
1
answer
682
views
Why is it not a good idea to run Shor's algorithm on a big noisy quantum computer?
Suppose I try to run Shor's algorithm on a big noisy quantum computer.
For a given input I repeat the circuit many times and collect statistics for the measurements of each qubit.
Now based on the ...
4
votes
3
answers
414
views
Why does making a quantum circuit more noise resilient make it easier to simulate classically?
I was reading Quantum Computing in the NISQ era and beyond (John Preskill, 2018) but I didn't get this point on pages 9-10:
There is a substantial opportunity for experimentalists and theorists, ...
- 143
4
votes
1
answer
461
views
What kind of errors does the master equation in the Lindblad form describe, continuous errors or discrete errors?
I noticed that in page 427 in Nielsen & Chuang's book Quantum Computation and Quantum Information, quantum error correction is possible because errors can be discretized.
In other hand, the ...
- 585
4
votes
1
answer
1k
views
How to calculate the average fidelity of Pauli error channel
This question is related to this and this.
I am working on Qiskit to design QEC schemes.
My model works with Pauli errors.
I would like to give to my Pauli error channel probabilities $p_x,p_y,p_z$ ...
- 2,058
4
votes
1
answer
314
views
Can quantum error correction work on any type of channel?
It says on wikipedia that quantum error correction can (at best) correct phase flips and bit flips. A popular form of representing a quantum channel is in its Kraus representation (scroll down to ...
- 1,459
4
votes
1
answer
71
views
How can I fit an unknown quantum channel?
Suppose that I have one noisy channel $\mathcal{E}$ and I want to fit it with another one $\mathcal{E}_0(p)$ that depends on some fitting parameter $p$.
As both of this processes for me are ...
- 77
4
votes
1
answer
507
views
Exponential Growth of Noise in Quantum Computers
I recently listened to a presentation for Introductory Quantum Computing. It was very general and meant to give the listeners an idea about the potential for Quantum Computing.
The speaker ended the ...
4
votes
1
answer
105
views
What is the explicit form of $T_1$ decay channel?
I see $T_1$ error mentioned in many experimental papers (for example, page $10$ of this paper mentions such a decay.)
How do I model $T_1$ decay theoretically? More concretely, here's my question. Say ...
- 1,515
4
votes
2
answers
634
views
How to intentionally add noise to a Qiskit circuit?
I am attempting to intentionally add noise to my qiskit circuit by applying n-pairs of CNOT gates. The effect of this should be to yield the same result of my baseline (no pairs of CNOT gates applied) ...
- 565
4
votes
1
answer
515
views
How to add noise to existing gates in Cirq?
I would like to add noise to existing gates in Cirq, i.e. to define something like
NewGate = cirq.Gate(qubit)
followed by
...
- 41
4
votes
1
answer
404
views
How to import noise model from IBM qiskit real device?
I am trying to import the noise model of an IBM 'large' device. I don't have access to the devices with more than 7 qubits so it doesn't allow me to import the backend and then do
...
- 55
4
votes
1
answer
70
views
Is it overestimating noise in a QPU if we use infidelities and also quantum channel such as depolarising or amplitude damping?
I have mainly seen two ways of studying noise in quantum algorithm simulation.
The first one is to suppose that your quantum gate can be implemented with a probability of success of $\mathcal{F}$ (...
- 126
4
votes
1
answer
32
views
If there is quantum noise, can a time interval be short enough that only one-qubit errors (eg. as in the Shor code) occur?
The Shor code can be used to protect against an arbitrary one-qubit error. If the time interval over which quantum noise acts is short enough, can it be assumed only one-qubit errors occur, so one ...
- 41
4
votes
1
answer
57
views
Is un-computing $U$ a good proxy for circuit fidelity?
I'm trying to estimate the fidelity of some family of unitaries $U(\theta)$ implemented on a noisy quantum computer. To do so, I start from an uninitialized state $|0\rangle$ and run the circuit $U(\...
- 7,646
4
votes
1
answer
105
views
Dephasing noise and error correction
It is my impression that $ Z $ errors are the dominant source of noise in many platforms used for quantum computing. For example, Ultrahigh Error Threshold for Surface Codes with Biased Noise says ...
- 4,916
4
votes
1
answer
627
views
Simulators vs Real Backends
I am using Qiskit to run some circuits and a question arises in my mind. I know that when we run in the simulators we are running in "ideal" environments. This means there is no noise that ...
- 41
4
votes
1
answer
1k
views
Is there any way we get the state vector/density matrix of a noisy simulation in qiskit?
In Qiskit we can't use noise models in the 'state vector_simulator' or the 'unitary simulator', hence making it impossible to compute fidelity of the output of the noisy circuit and the noiseless ...
