22 votes

Is error correction necessary?

That doesn't scale well. After a moderately long calculation you're basically left with the maximally mixed state or whatever fixed point your noise has. To scale to arbitrary long calculations you ...
M. Stern's user avatar
  • 2,422
15 votes
Accepted

How good is basic_device_noise_model() simulating the noise in the quantum computer?

There is no specific paper for this, though information on the model can be found in the Qiskit Aer API documentation and is based on the research of IBMQ quantum computing group. As examples you can ...
cjwood's user avatar
  • 1,221
14 votes

Is error correction necessary?

If the error rate were low enough, you could run a computation a hundred times and take the most common answer. For instance, this would work if the error rate were low enough that the expected number ...
Niel de Beaudrap's user avatar
14 votes
Accepted

What exactly is meant by "noise" in the following context?

As an addition to Nat's answer, it's worth mentioning that 'noise' is a specific concept1 in quantum computing. This answer will use Preskill's lecture notes as a basis. In essence, noise is indeed ...
Mithrandir24601's user avatar
  • 3,686
11 votes

What exactly is meant by "noise" in the following context?

Unfortunately for analog computation it turns out that when realistic assumptions about the presence of noise in analog computers are made, their power disappears in all known instances; they cannot ...
Nat's user avatar
  • 1,497
10 votes
Accepted

How does approximating gates via universal gates scale with the length of the computation?

Throughout this answer, the norm of a matrix $A$, $\left\lVert A\right\rVert$ will be taken to be the spectral norm of $A$ (that is, the largest singular value of $A$). The solovay-Kitaev theorem ...
Mithrandir24601's user avatar
  • 3,686
10 votes

Which quantum error correction code has the highest threshold (as proven at the time of writing this)?

As far as I’m aware, the surface code is still regarded as the best. With an assumption of all elements failing with equal probability (and doing so in a certain way) it has a threshold of around 1%. ...
James Wootton's user avatar
10 votes
Accepted

How to selectively apply noise in Qiskit simulations?

Yes you can: When you build a noise model the noise is defined with respect to the name or label of gate objects, so you can use the labelto create multiple versions of a single gate but reference ...
cjwood's user avatar
  • 1,221
10 votes
Accepted

Why is it not a good idea to run Shor's algorithm on a big noisy quantum computer?

Factoring a 2048 bit number with Shor's algorithm involves performing one billion Toffoli gates under superposition (ref). Suppose your superposed Toffoli gate error rate is an amazing 0.01%. Note ...
Craig Gidney's user avatar
  • 37.1k
9 votes
Accepted

Degradable channels and their quantum capacity

A channel $\Phi$ is said to be degradable if there exists another channel $\Xi$ such that $\Xi\Phi$ is complementary to $\Phi$. The idea here is as follows. Suppose $\Phi$ is a channel and $\Psi$ is ...
John Watrous's user avatar
  • 5,907
8 votes
Accepted

What is the clear definition of coherent versus incoherent errors?

Coherent vs incoherent: as a rule of thumb, coherent is unitary, incoherent is stochastic. The distinction is not entirely clear when your channel is a mixture of these. Thus, it makes sense to ...
Balint Pato's user avatar
7 votes
Accepted

How do quantum computers prevent "quantum noise"?

How do we prevent quantum noise in a quantum computer? Well, technically the answer is (at least for most systems): we use ridiculously low temperatures (much colder than space), we shield everything ...
3244611user's user avatar
7 votes

Depolarizing channel implementation on IBM Q

There are several ways that you could realise the depolarising map $ \mathcal N_p(\rho) = (1\!-\!p)\:\!\rho + p \!\!\:\cdot\!\tfrac{1}{2}\mathbf 1$ map on a quantum computer — including an ...
Niel de Beaudrap's user avatar
7 votes

Which quantum error correction code has the highest threshold (as proven at the time of writing this)?

I believe that the Centre for Engineered Quantum Systems, School of Physics, The University of Sydney and the Center for Theoretical Physics, Massachusetts Institute of Technology use of a tensor ...
whurley's user avatar
  • 529
7 votes

How can noise on a device be simulated using measured noise parameters?

This can be done using the 'Aer' component of Qiskit. The properties information can be turned into a noise model using ...
James Wootton's user avatar
7 votes
Accepted

Incorporating idling errors while using stim

No, there's no simple built-in way. You have to do it for yourself. This was an intentional design choice, which I will now attempt to justify because I do realize it's inconvenient. Stim has no ...
Craig Gidney's user avatar
  • 37.1k
7 votes
Accepted

Is it possible to use fake backends to run Qiskit Runtime primitives?

Using primitives with fake backends You can use BackendEstimator to work with fake backends. As primitives implementation, ...
Egretta.Thula's user avatar
6 votes
Accepted

What kind of errors does the master equation in the Lindblad form describe, continuous errors or discrete errors?

The errors that are described by the Master equation are continuous errors. The action of error correction is to discretize those errors. For example, dephasing noise can be described by the Master ...
DaftWullie's user avatar
  • 58.1k
6 votes
Accepted

IBM Q calibration parameters

frequency (GHz): The frequency(energy) associated with the transition between the qubit's ground state ($|0\rangle$) and first excited state ($|1\rangle$). readout error: The probability of preparing ...
ThomasAlexander's user avatar
6 votes
Accepted

Why attenuator and not filters for QC driving line

(1) Both filters and attenuators are used Let me just start by saying that non-attenuating filters have not been completely ruled out by people working in the design of cold quantum computers. I will ...
user1271772 No more free time's user avatar
5 votes
Accepted

Is it true that observing a quantum state will end the superposition of states? How can I not observe?

I'm going to go for an intuitive answer here, as requested. Let's s go in steps: Your input is (often?) classical, so up to that point we're good. Then you start doing quantum operations and achieve, ...
agaitaarino's user avatar
  • 3,827
5 votes
Accepted

Exponential Growth of Noise in Quantum Computers

According to so-called threshold theorem, it is possible to get rid of errors in quantum computation with arbitrary precision. However, there is an assumption that you have enough qubits. To ...
Martin Vesely's user avatar
5 votes

How to not optimize the quantum gates in a qiskit circuit when running it in the real device?

Optimization level 0 does not perform 1 qubit gate optimization and it will send 2 X gates (well 2 U3 gates after it unrolls to the basis set). You can see the passes optimization level 0 runs here: ...
Matthew Treinish's user avatar
5 votes
Accepted

Why should we use density matrices to simulate quantum systems with noise?

Noise effects introduce classical uncertainty in what the underlying state is. A mixed state is a statistical ensemble of several quantum states $|\psi_i\rangle$ (not necessarily orthogonal), with ...
Michele Amoretti's user avatar
5 votes

Is spontaneous excitation possible?

As a first note: the (uncontrolled) transition of $|1\rangle$ to $|0\rangle$ is generally not referred to as dephasing but as relaxation. The noise-process that involves (spontaneous) relaxation is ...
JSdJ's user avatar
  • 5,469
5 votes
Accepted

How can I fit an unknown quantum channel?

The 2-norm difference typically isn't particularly physical. So no, this is most likely not the right distance. What you want from a physical point of view is a distance measure which measures the ...
Norbert Schuch's user avatar
5 votes
Accepted

Can quantum error correction work on any type of channel?

For any quantum error correcting code, it is possible to construct a channel which introduces errors that the code cannot correct. However, the key point is that such channels are highly adversarial ...
Adam Zalcman's user avatar
  • 22.3k
5 votes

How are eavesdroppers detected when using BB84 in the presence of noise?

The standard noisy approach is not to try to determine the presence of an eavesdropper as such, but to create a final key where, even if there is an eavesdropper, you can still be confident that the ...
GotCarter's user avatar
  • 401
4 votes

Is error correction necessary?

noise should average itself out. Noise doesn't perfectly average itself out. That's the Gambler's Fallacy. Even though noise tends to meander back and forth, it still accumulates over time. For ...
Craig Gidney's user avatar
  • 37.1k

Only top scored, non community-wiki answers of a minimum length are eligible