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Questions tagged [experiment]

For questions related to experiments with actual quantum computing devices and how to interpret their results. Also appropriate if the question can only be reasonable answered with an experiment (or experiment design).

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When is a quantum algorithm considered to have a significantly superior performance over another quantum algorithm?

Suppose we have two heuristic quantum algorithms $A$ and $B$ that attempt to solve a certain class of optimization problems. Let's suppose that the benchmarking metric is Time To Solution (TTS), which ...
MonteNero's user avatar
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1 vote
1 answer
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What is the purpose of Doppler cooling in neutral atom devices?

As a theorist without much experimental physics background, I am reading some reviews to understand how these systems work. I've learned that one needs to use Doppler cooling before trapping the atoms ...
Will Yang's user avatar
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2 votes
1 answer
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Randomness and precision of Quantum Number Random Generators

I am reading about the problem of generating random quatum numbers, and I am interested in the state of the art in terms of the true randomness these generators achieve. As far as I know, following ...
Martin Hurtado's user avatar
4 votes
2 answers
118 views

Is quantum energy teleportation a specific version of quantum teleportation?

I just read another sensationally titled article in Quanta magazine, Physicists Use Quantum Mechanics to Pull Energy out of Nothing where they discuss the work of Masahiro Hotta on transferring energy ...
Mauricio's user avatar
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8 votes
0 answers
259 views

What is a gate-level circuit used in the 2022 Jafferis et al. experiment on Sycamore?

A recently published Nature paper of Jafferis et al. describes an experiment with a handful of qubits performed on Google's Sycamore processor to explore the SYK model in the context of AdS/CFT and ...
Mark Spinelli's user avatar
5 votes
1 answer
130 views

Does it make sense to compare different quantum computer technologies?

Let's assume I have some quantum program I tested and tuned on a simulator and that now I want to see how it actually performs on real quantum hardware. I test it on IBM Superconducting devices and ...
mpro's user avatar
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7 votes
1 answer
254 views

Publicly available samples for quantum circuits and/or simulators

With Yosi Rinott and Tomer Shoham we studied various statistical aspects of samples coming from NISQ computers. My question is about available data consisting of samples from NISQ computers We would ...
Gil Kalai's user avatar
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1 answer
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Is there an alternative algorithm to extract a probability of states of qubit after measuring?

Let a simple quantum circuit consist of one qubit and one classical bit. Initially, a qubit has the $|0\rangle$-state and then goes through some sequence of quantum gates, see the circuit below. The ...
SFriendly's user avatar
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1 answer
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Suggestion on reading resources on superconducting quantum computing

I am a physics student who works with NMR spin-based quantum computing, now branching into superconductor-based qubits. So I am reading lecture notes by Nathan K Langford and Steve Girvin. I can ...
iamram's user avatar
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3 votes
1 answer
182 views

Can the paper by Monz et al. (2015) be regarded as a real implementation of Shor's algorithm?

I'm studying about the Shor algorithm and I wonder whether the paper below can be regarded as a real implementation of the Shor algorithm: https://arxiv.org/abs/1507.08852 In this paper, they tried to ...
Alex's user avatar
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2 votes
1 answer
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Good review articles on microwave hardware for superconducting qubit quantum computing?

I am trying to find some review articles on the microwave hardware used in superconducting qubit quantum computing. So far, most papers that I found seem to be high level overviews, e.g., Multilayer ...
LearnerAL's user avatar
5 votes
1 answer
172 views

How big is the Hilbert space of a boson sampling experiment?

Boson sampling experiments are typically characterized by two key parameters: the number of photons $M$ and the number of modes $N$. A recent experimental demonstration (arXiv:2106.15534) with $M = ...
tparker's user avatar
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3 votes
2 answers
496 views

'Internal error. Error code 9999' when running job on IBMQ

I'm trying to run a series of circuits in a job and I keep getting this error message which I haven't been able to find the meaning of anywhere in qiskit's documentation, online, etc. The job appears ...
Mykolas Sveistrys's user avatar
5 votes
1 answer
88 views

Can entangled photons create entanglement in material particles?

Is it possible that two entangled photons when absorbed by two material particles, say two atoms, lead to the entanglement of these atoms? Is there any published research on this topic?
User101's user avatar
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How to quantify trace distance between two matrices representing two quantum optical networks?

This is my first post here, so I'm sorry if this question could be ill-formulated. I have performed measurements on a 12x12 optical quantum network, so that I have a stochastic matrix $P^{exp}$ where ...
v_enushk's user avatar
1 vote
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80 views

Working with higher energy states in Qiskit Experiments

I'm looking at the source code for the Qiskit Experiments module and see that the EFRabi class subclasses the Rabi class with the intent of calibrating rotations between the 1 and 2 states instead of ...
QuantumLearner's user avatar
3 votes
0 answers
82 views

Why is it important to perform optical quantum computing with ONLY linear components?

The main achievement of the KLM protocol is demonstrating that quantum computing can be done with only linear optical elements, i.e., beam splitters, phase shifters, single-photon sources, and photo-...
LearnerAL's user avatar
1 vote
1 answer
132 views

In the job tab, no histogram appears

(Newbie here) Accessing IBM Q Experience on a Windows 7 operating system and using the Google Chorme browser. I can completely assemble my circuit, using the IBM Quantum Composer and when executing it ...
Ikky R's user avatar
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1 vote
1 answer
56 views

How can I resolve this get_count issue from running multiple circuits?

I'm running a couple of circuits at the same time using an array of variables. However, I met an issue regarding accessing the counts. Here's part of the code I have: ...
ZR-'s user avatar
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1 vote
1 answer
207 views

Return outputs with zero counts

I am running a simple 3 qubit circuit which produces the following results: {'000': 5, '001': 3, '010': 10, '100': 5, '101': 7, '110': 7, '111': 4} There are no ...
LOC's user avatar
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3 votes
0 answers
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Is there a measurable of entanglement for a many-body system?

After having a discussion with a quantum computing colleague, a question came up: is there any meaningful way to measure entanglement (or something related to it) in a solid-state many body system ...
Dr. T. Q. Bit's user avatar
4 votes
0 answers
61 views

What is the executable opcode for Qiskit quantum hardware, as the quantum circuits or the transpiled/compiled QObj/ QASMQObj are assembly languages? [duplicate]

When we write a QASM code or build quantum circuit on Qiskit GUI, it converts it into QObj/QASMQObj (refering paper Qiskit Backend Specifications for OpenQASM and OpenPulse Experiments) or its ...
Shampa Sarkar's user avatar
1 vote
1 answer
320 views

What experiments can distinguish between mixed and pure states?

To distinguish between a coherent and de-cohered stage of the same system what experiments can provide the answer? The term Experiment is used here in the Bohr-Einstein-debate sense, a realizable ...
MusashiK's user avatar
2 votes
0 answers
67 views

Where does the energy go in a Power Rabi experiment with superconducting circuits?

When performing a Power-Rabi experiment, e.g in superconducting circuits, we are playing a pulse to a qubit and then reading out its state by playing another pulse to a dispersively-coupled readout ...
Qexp's user avatar
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0 answers
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What does "decoherence attenuates the density matrix" mean?

I'm reading the paper Implementation of the Quantum Fourier Transform. On page 4, they write To a first approximation, decoherence during the course of the QFT attenuates the entire density matrix. ...
NNN's user avatar
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8 votes
2 answers
1k views

Changing one qubit causes changes in another independent qubit on ibmqx2 in IBM Q Experience

When I run this program on ibmqx2 (the backend matters) in IBM Q Experience, the results are interesting. Essentially, the program measures the error rate on $|q_0\rangle$ after fiddling with $|q_1\...
balios's user avatar
  • 137
3 votes
1 answer
101 views

Writing twice to same classical register -> 1 for some backends in IBM Q Experience

On some backends, measuring the same expected value twice to the same classical register always leaves that classical register in the "1" state. I don't know if these results will hold over time, but ...
balios's user avatar
  • 137
6 votes
1 answer
203 views

Reversal of time arrow on IBM Q

It is well known that a quantum computer is reversible. This means that it is possible to derive an input quantum state $|\psi_0\rangle$ from an output $|\psi_1\rangle$ of an algorithm described by a ...
Martin Vesely's user avatar
2 votes
2 answers
152 views

Simple program produces consistently skewed results in IBM Q Experience

I'm running this program (essentially a two bit random number generator) on ibmqx2 in IBM Q Experience. The backend matters. Other machines give unexpected results, but the graph looks different for ...
balios's user avatar
  • 137
1 vote
1 answer
320 views

What is the difference between classical and quantum computers as well as computing (permuting) itself?

Theoretically and for sure physically (I know the quantum physics behind it) I know something about it. But not that much. That's why I ask the question here. I'm very interested. The only answer to ...
Deschele Schilder's user avatar
2 votes
0 answers
25 views

Is manual or automated error correction more practically promising in the near term?

I'm curious if there's any consensus on this question among actual practitioners, but please feel free to close it if it's hopelessly opinion-based (since we've only taken baby steps toward the ...
tparker's user avatar
  • 2,357
5 votes
3 answers
3k views

Quantum Supremacy: Some questions on cross-entropy benchmarking

I was skimming through the Google quantum supremacy paper but got stuck on this section: For a given circuit, we collect the measured bit-strings $\{x_i\}$ and compute the linear XEB fidelity [24-26, ...
Björn Smedman's user avatar
1 vote
1 answer
310 views

given an EPR pair, how do I calculate expectation value?

given A and B share EPR pairs $ (|00⟩+|11⟩)/√2$ both are free to measure their own qubit with the following measurement settings A measures with $[ |0⟩, |1⟩ ]$ B measures with $[ sin(3π/8)|0⟩ + cos(...
Win's user avatar
  • 11
3 votes
1 answer
552 views

IBM's quantum computing capabilities — entangled 18-qubit GHZ states and high coherence times

Here's a blog post that corresponds with what IBM presented at the 2019 March Meeting. In this post, they claim they've measured qubit T1 relaxation times above 500 microseconds, and claim that they'...
psitae's user avatar
  • 1,300
3 votes
0 answers
131 views

Measuring Ising anyons: What is a fusion measurement?

I have several doubts about measuring Ising anyons. Measurement is crucial for quantum computation and even more so for magic state distillation which is necessary to make Ising anyons universal. ...
Marsl's user avatar
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3 votes
0 answers
33 views

Can one make NV centred type qubits from analogus materials in the periodic table?

Can one replace Nitrogen with Phosphorus and Carbon with Silicon and so on? What would be the conditions that would preclude such a realisation? Are there any implemenations so far?
Tejas Shetty's user avatar
3 votes
0 answers
45 views

Spin precession using a laser

According to Christopher Monroe: "Modular Ion Trap Quantum Networks: Going Big", the hyperfine states of the valence electron in the Yb+ is used as a qubit. I know that we can change the spin ...
Tech Solver's user avatar
3 votes
0 answers
68 views

Can "experimental data from a quantum computer" be used to test separability probability conjectures?

An article entitled "Experimental data from a quantum computer verifies the generalize Pauli exclusion principle" by Scott E. Smart, David I. Schuster, and David A. Mazziotti has just appeared In the ...
Paul B. Slater's user avatar
4 votes
1 answer
90 views

What is the significance of recent demonstration of a passive photon–atom qubit swap operation?

In reference to this recent nature article: https://www.nature.com/articles/s41567-018-0241-6 Specifically, does this warrant a new type of gate?
artha's user avatar
  • 388
15 votes
2 answers
1k views

State of the art gate speeds and decoherence times

I am interested in the state of the art gate speeds and decoherence times for the qubit types I know are being pursued by companies presently: superconducting qubits, ion trap qubits, photonic qubits....
user1271772's user avatar
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7 votes
2 answers
197 views

Breakthroughs in quantum computing using non-standard quanta [closed]

It seems that quantum computers can be classified by the type of quantum they operate on. Not entirely sure what category most common current systems fall into (eg. D-Wave, Google, IBM, Microsoft). ...
user820789's user avatar
  • 3,272
20 votes
1 answer
580 views

Is "probabilitistic,universal, fault tolerant quantum computation" possible with continuous values?

It seems to be a widely held belief within the scientific community that it is possible to do "universal, fault-tolerant" quantum computation using optical means by following what is called "linear ...
rrtucci's user avatar
  • 679
6 votes
3 answers
198 views

Will Moore's Law be no longer effective once quantum computers are created? [duplicate]

Moore's law states that computer power doubles in every 18 months (more formally: "the number of transistors in a dense integrated circuit doubles about every two years."). Statistics suggest that ...
Archil Zhvania's user avatar
11 votes
2 answers
2k views

Rotating about the y- or z-axis of the Bloch sphere

In order to rotate about an axis of the Bloch sphere we ususally use pulses e.g. in trapped ion quantum computing or superconducting qubits. Let's say we have rotation around the x-axis. What do I ...
Quasar's user avatar
  • 263
5 votes
1 answer
224 views

Conditional Phase Gate Superconducting Qubits

In the paper "Demonstration of two-qubit algorithms with a superconducting quantum processor" (L. DiCarlo et al., Nature 460, 240 (2009), arXiv) they demonstrate how to realize conditional phase gates ...
Quasar's user avatar
  • 263
5 votes
0 answers
66 views

Is PostBQP experimentally relevant? [duplicate]

Far from my expertise, but sheer curiosity. I've read that PostBQP ("a complexity class consisting of all of the computational problems solvable in polynomial time on a quantum Turing machine with ...
agaitaarino's user avatar
  • 3,747
25 votes
2 answers
608 views

What is the status of confirming the existence of anyons?

In a comment on my answer to the question: What exactly are anyons and how are they relevant to topological quantum computing? I was asked to give specific examples of occurrence of anyons in nature. ...
user1271772's user avatar
  • 12.8k
7 votes
1 answer
122 views

Translation of color/toric code to a small network of solid-state spins

Within Quantum Error Correction and stabilizer codes, toric codes/surface codes are very tempting, mainly for their high error threshold. For more background please check up, in our Physics sister (...
agaitaarino's user avatar
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12 votes
0 answers
109 views

Active improving of nanodiamond surfaces for NV centers?

This question is related (and complementary) to "Passive improving of nanodiamond surfaces for NV centers?". Nitrogen-Vacancy centers (NVs) have astonishing quantum properties, which make them ...
agaitaarino's user avatar
  • 3,747
5 votes
1 answer
114 views

Passive improving of nanodiamond surfaces for NV centers?

Nitrogen-Vacancy centers (NVs) have astonishing quantum properties, which make them interesting as potential hardware both for quantum computing in particular and for quantum technologies in general. ...
agaitaarino's user avatar
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