Questions tagged [nisq]

For questions related to Noisy Intermediate Scale Quantum (NISQ) computing. NISQ computers cannot be classically simulated in a reasonable time but are not advanced enough to also be error corrected.

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Can ancilla-based parity measurements be used to detect errors in NISQ algorithms?

Measuring stabilizer eigenvalues is a fundamental part of quantum error correction. However, I was wondering if the idea of measuring a stabilizer using an ancilla could be useful in other contexts as ...
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7 votes
1 answer
108 views

What use cases are there for 127 qubit QPUs?

IBM have recently announced their 127 qubit Eagle processor. Other approaches, such as Rydberg arrays, have now 256 qubits, as for example in QuEra's QPU QPU. While these are without a doubt ...
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2 answers
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Is it possible to efficiently measure outer products of quantum states, of the form $|a\rangle\langle b|$?

I am looking at a matrix reconstruction algorithm that, given singular values $\sigma_i$ and quantum states $|u_i\rangle$ and $|v_i\rangle$ that are efficiently prepared on a quantum computer, ...
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6 votes
0 answers
139 views

Could the Hamiltonian of a 2x2 Rubik's Cube be simulated with a NISQ device?

Consider the four cells on each of the six faces of the 2x2x2 Rubik's cube (the pocket cube). We can construct and simulate a quarter-turn Hamiltonian as below. $^*$ Let $\langle F_1,U_1,R_1\rangle$ ...
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  • 6,777
2 votes
1 answer
44 views

Mahadev's classical homomorphic encryption for quantum circuits and NISQ computing

I'm currently reading Mahadev's paper Classical Homomorphic Encryption for Quantum Circuits: https://arxiv.org/abs/1708.02130 I was told that Mahadev's scheme is not something that can be implemented ...
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1 vote
0 answers
38 views

How do you quantify the figurative 'cost' of a quantum circuit

Many gates are not available on a real computer and therefore the circuit must be transpiled into a specific set of gates. I have seen this equation below which is used to to determine the 'cost' of a ...
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  • 77
8 votes
0 answers
127 views

Definition of a NISQ device with respect to qubit counts and error rates

How do we define whether a device is a noisy intermediate-scale quantum (NISQ) device with respect to number of qubits and their error rates? Does it make sense to do this? I believe I once saw a ...
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3 votes
1 answer
107 views

What is the "quantum mean value problem"?

What is the "Quantum mean value problem"? A definition I found was that it is "estimating the expected value of the tensor product observable on the output state of a quantum circuit&...
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2 votes
1 answer
65 views

Design NISQ Circuit with StrawberryFields

I am trying to design this circuits with strawberry fields. However I could not connect my first and second qubit mode: orange boxes are beam splitters, blue boxes are phase shifters. The green box ...
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  • 406
1 vote
2 answers
99 views

What are the libararies for Machine Learning on NISQ Chip? And What are the roadmaps?

Nowadays quantum learning is hiring. And we can see mainly two different area. One of them is variational algorithms part. And the other one is classical learning for quantum systems like NISQ. (Some ...
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  • 406
2 votes
2 answers
156 views

Quantum Machine Learning in NISQ era

I know that quantum algorithms can be useful for machine learning ("ML") methods, and vice versa. For example if we use QAOA we can use for the optimization part different types of ML ...
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4 votes
1 answer
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Gate SWAP vs Physical SWAP in Trapped Ions for chain reordering

In trapped ion quantum computers, especially in systems with multiple traps, you may need at some point to perform a "chain reordering", in which you change an ion's position within the ion ...
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3 votes
1 answer
40 views

NISQ algorithm: do they all have circuit updated between each run AND impossible to predict when they will stop?

I don't know very much the NISQ algorithms, but the ones that I know are based on kind of "Hybrid" calculation between a quantum computer and a classical computer. Indeed, for instance in ...
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1 vote
1 answer
67 views

Why is the VQE insensitive to noise?

I was going through the Grove documentation on the Variational Quantum Eigensolver. In one of the demonstrations with noisy gates, it is seen that resulting eigenvalue is quite close to the expected ...
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3 votes
1 answer
101 views

What is the implication of locality in QAOA?

Suppose I am solving the TSP formulated as a QUBO problem using QAOA. I understand from the original paper that there is a parameter $p$ which sets the number of steps used in the alternating ansatz. ...
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3 votes
1 answer
136 views

How is back-propagation done in "Transfer learning in hybrid classical-quantum neural networks"

Just read this paper from Xanadu on Quantum Transfer Learning and a couple of things are unclear to me regarding the optimisation step. How is back-propagation done through the classical weights ...
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6 votes
1 answer
313 views

What's the point of VQE if classical computers can solve for eigenvalues easily?

From a few VQE tutorials online I see that they normally start with something like: VQE is a way of getting a good estimate for the upper bound of the ground state of a quantum system's Hamiltonian....
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2 votes
1 answer
156 views

Will NISQ based algorithms be useful in fault-tolerant Quantum computers?

As a data scientist, I want to use the cutting edge algorithms of machine learning to build my models, I am interested in quantum machine learning, the recent research in QML is about variational ...
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2 votes
0 answers
37 views

Dealing with noise in NISQ

I wanted to know if there are some way in NISQ (we run "bare" gate without Q.E.C) to certify if an algorithm will give a correct or wrong answer based on the process of a single gate ? For example in ...
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7 votes
0 answers
232 views

What are the "nice" properties of the diamond norm and why is it used?

I have heard about the diamond norm, and from what I understood it is a "nice" tool to quantify quality of quantum gates in the NISQ era. I would like to know a little more before going in detail in ...
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3 votes
1 answer
574 views

Quantum speedup in Bayesian machine learning on NISQ computers

It is well known that in Bayesian learning, applying Bayes' theorem requires knowledge on how the data is distributed, and this usually requires either expensive integrals or some sampling mechanism, ...
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5 votes
3 answers
2k views

Pennylane and Qiskit for quantum machine learning

I'm interested in quantum computing, specifically in “quantum machine learning” (QML). I'm going to start my masters program in computer science and have previous experience in classical machine ...
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3 votes
0 answers
79 views

Active areas of research for NISQ algorithms

What areas of research in NISQ algorithms have heavy focus? I'm interested in quantum chemistry algorithms because of previous work (e.g. VQEs), and I'd love to learn more about other near-term ...
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1 vote
2 answers
138 views

Software for Quantum Computing

From what I read classical computing evolved so quickly because of the funding-applications cycle. Even though the cost to make denser IC's was increasing rapidly, the applications were also getting ...
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7 votes
1 answer
198 views

Most efficient way for general state generation

Assume we are given an $n$-qubit system and complex numbers $a_0, \ldots, a_{m-1}$ with $m = 2^n$. Assume further we start with the initial state $|0 \ldots 0\rangle$ and want to make the ...
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  • 171
5 votes
1 answer
177 views

Where does the Xmon simulator from Googles cirq framework its entropy from?

Measurements create entropy as we all know. But computers themselves are deterministic machines. Most devices use processor heat as a source for random number generation as far as I know - which has ...
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  • 157
10 votes
1 answer
264 views

Minimum number of CNOTs for a 4-qubit increment on a planar grid

Recently I've been wondering how high NISQ machines will be able to "count". What I mean by that is, given the most optimized increment circuit you can make, how many times can you physically apply ...
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15 votes
4 answers
749 views

What use has quantum computing been?

Most of us on this site believe that quantum computing will work. However, let's play devil's advocate. Imagine that we suddenly hit some fundamental stumbling block that prevented further development ...
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11 votes
1 answer
297 views

Devising "structured initial guesses" for random parametrized quantum circuits to avoid getting stuck in a flat plateau

The recent McClean et al. paper Barren plateaus in quantum neural network training landscapes shows that for a wide class of reasonable parameterized quantum circuits, the probability that the ...
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50 votes
1 answer
12k views

What is meant by "Noisy Intermediate-Scale Quantum" (NISQ) technology?

Preskill introduced recently this term, see for example Quantum Computing in the NISQ era and beyond (arXiv). I think the term (and the concept behind it) is of sufficient importance that it deserves ...
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  • 3,587
14 votes
4 answers
927 views

How should different quantum computing devices be compared?

In the last years, there has been a spur of demonstrations of devices able to perform proof of principle, small-scale, non-fault-tolerant quantum computation (or Noisy Intermediate-Scale Quantum ...
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