Questions tagged [gate-fidelity]
16 questions
9
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
- 171
- 1
- 4
6
votes
2 answers
Is it possible to have a trace fidelity of 1 even if two unitary operations are different?
The gate fidelity of two quantum unitary operations is often described using $\frac{1}{2^n}|\text{tr}(U^\dagger V)|$. Is it ever possible that $U^\dagger V \ne I$ however $\frac{1}{2^n}|\text{tr}(U^\dagger V)| = 1$? Specifically, is it possible to…
smi
- 163
- 6
6
votes
1 answer
Is there a concentration inequality for the quantum gate fidelity $F(C,U)$ for a channel $C$ such that $\int dU F(C,U)=X$?
For a fixed quantum channel $N$ and a unitary channel $U$, we define $N$'s gate fidelity as
$$ F(N,U) = \int \langle \psi| U \, N(| \psi \rangle \langle \psi |) \, U^\dagger| \psi \rangle d\mu_H(\psi)$$
where $\mu_H$ is the Haar measure over…
Davide Li Calsi
- 63
- 3
5
votes
2 answers
What is a difference between error rates and qubit/gate fidelity?
What is a difference between error rates and qubit/gate fidelity? A bit of maths in the explanation is fine but I am an A Level student doing a research project so definitions would be preferred.
980emma
- 53
- 3
4
votes
1 answer
What is the relationship between gate fidelity and norm?
I've seen a lot of analyses on quantum circuit error bound based on the norm difference $\Vert U - V \Vert$.
On the other hand, I've also seen a lot of papers that use the gate fidelity $\frac{1}{2^n}\lvert \text{tr}(U^\dagger V) \rvert$.
Is there a…
user185671631
- 127
- 5
4
votes
1 answer
Can you compute the average fidelity of two qubits by averaging over a finite number of states?
For a single qubit and a quantum operation, the fidelity
$$
F_{|\psi\rangle\!\langle \psi|} = \mathrm{Tr}\bigg(U | \psi \rangle\!\langle \psi | U^\dagger \mathcal M\big(| \psi \rangle\!\langle \psi |\big)\bigg),
$$
averaged over all possible initial…
Omar Nagib
- 141
- 1
4
votes
0 answers
Qiskit NoiseModel.from_backend gives wrong gate error
According to the Qiskit documentation, a gate error is simulated by a thermal relaxation channel followed by a depolarisation channel, where the parameter of the depolarisation channel is adjusted so that the average gate infidelity corresponds to…
siserman
- 161
- 3
4
votes
0 answers
How can I get fidelity of a gate from randomized benchmarking?
I found (page 33) the method of finding fidelity from fit by "interleaved and reference decay" according to the sequence fidelity formula: $$F_{ref}=Ap_{ref}^{m}+B,$$
where $p_{ref}^{m}$ is sequence decay.
But if we look at the following…
Curious
- 319
- 2
- 7
3
votes
0 answers
Averaging over Haar measure with projectors in the context of 2-qubit states
The paper https://arxiv.org/abs/2407.20184 deals with calculating the so-called filter function capturing the sensitivity of the fidelity of a quantum channel to the power-spectral-density of a noise source within linear response theory. If the…
eranreches
- 131
- 2
3
votes
1 answer
Does any quantum channel satisfy ${\rm Tr}(\mathcal E^\dagger \mathcal E) \in[0, d^2]$?
I am reading the paper "Direct Fidelity Estimation from Few Pauli Measurements".
According to the paper, the entanglement fidelity between the a unitary channel $\mathcal U$ and a quantum channel $\mathcal E$, is defined as
\begin{align}
F_e = {\rm…
Michael.Andy
- 599
- 3
- 8
2
votes
1 answer
What are the "higher moments" of the gate fidelity?
Reading the paper Gate fidelity fluctuations and quantum process invariants I came across the concept of higher moments of the gate fidelity, for example in the following excerpt from the introduction:
In this paper, we calculate the variance of…
epelaez
- 2,985
- 1
- 9
- 31
1
vote
0 answers
Why do these two circuits have different noisy expectation values?
Consider the following two quantum circuits, which are both equivalent to identity:
These circuits have the same structure, but the $X$ and $\sqrt{X}$ gates are swapped.
Suppose we simulate these circuits under a depolarizing noise model, with…
htj
- 378
- 1
- 10
1
vote
0 answers
Typical coherent error over- / underotation values
I am thinking about coherent errors when applying quantum gates. As far as I have read, those are somehow more problematic than incoherent errors since they accumulate quadratically while incoherent errors accumulate linearly. Anyway, I guess that…
Josu Etxezarreta Martinez
- 4,136
- 15
- 42
1
vote
0 answers
Is there an upper bound on two-qubit fidelity improvements?
The higher the two-qubit fidelity, the lower the overhead for quantum error correction. This is especially preferable due to the fact that cheap QRAM would be useful for practical applications, QRAM is expensive due to error correction, and…
Victory Omole
- 2,332
- 1
- 10
- 24
1
vote
1 answer
Calculate average fidelity of QobjEvo
I am using QuTip to simulate a quantum gate, and I want to calculate the average fidelity of the gate.
I have the Hamiltonian, the interaction time, and Liouvillian modeling the decoherence.
Is there any easy way that I can get average fidelity from…
user26199
- 11
- 1