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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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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 ...
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5 votes
1 answer
137 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 = ...
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1 vote
1 answer
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'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 ...
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5 votes
1 answer
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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?
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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 ...
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1 vote
0 answers
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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 ...
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3 votes
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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-...
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Exacting specific results in running a list of tomography circuit

I run a test on tomography of two circuits like this: ...
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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 ...
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1 vote
1 answer
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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: ...
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0 votes
1 answer
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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 ...
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3 votes
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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 ...
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4 votes
0 answers
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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 ...
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0 votes
2 answers
131 views

Mixed state vs superposition , experiment test

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 ...
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2 votes
0 answers
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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 ...
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3 votes
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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. ...
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8 votes
2 answers
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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\...
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3 votes
1 answer
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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 ...
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5 votes
1 answer
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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 ...
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2 votes
2 answers
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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 ...
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1 vote
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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 ...
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2 votes
0 answers
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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 ...
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5 votes
3 answers
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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, ...
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1 vote
1 answer
227 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(...
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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'...
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3 votes
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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. ...
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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?
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3 votes
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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 ...
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3 votes
0 answers
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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 ...
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4 votes
1 answer
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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?
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13 votes
2 answers
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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....
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7 votes
2 answers
188 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). ...
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20 votes
1 answer
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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 ...
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6 votes
3 answers
184 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 ...
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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 ...
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5 votes
1 answer
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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 ...
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5 votes
0 answers
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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 ...
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24 votes
2 answers
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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. ...
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7 votes
1 answer
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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 (...
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11 votes
0 answers
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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 ...
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5 votes
1 answer
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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. ...
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7 votes
1 answer
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In qubit/qudit terms, where is the experimental limit between S=3/2 and 2·S=1/2?

This question is inspired by "What is the difference between a qudit system with d=4 and a two-qubit system?", as an experimental follow-up. Consider for illustration these two particular cases: ...
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19 votes
2 answers
394 views

Quantum simulation of environment-assisted quantum walks in photosynthetic energy transfer

This question is related to Can the theory of quantum computation assist in the miniaturization of transistors? and Is Quantum Biocomputing ahead of us? About 10 years ago, several papers discussed ...
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8 votes
2 answers
457 views

Which is the highest number factorized by QC in a non-specific experiment?

Since the original experimental contribution using the Shor's factoring algorithm to factorize the integer 15 some experiments have been performed in order to calculate the largest factorized number. ...
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6 votes
1 answer
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What are the current solutions to generate entangled qubits in the solid state?

Pairs of entangled qubits (or Bell pairs, or EPR pairs) are a fundamental resource for quantum computing, in the sense that any computational platform that cannot generate entanglement will also be ...
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4 votes
1 answer
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Any few-qubit versions of Lloyd's "weakly-coupled-array" quantum computing?

On 1993, Seth Lloyd published in Science a proposal for A Potentially Realizable Quantum Computer. In a nutshell, this consists in a long chain of weakly coupled qubits which are operated with (almost)...
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13 votes
2 answers
997 views

What is the longest time a qubit has survived with 0.9999 fidelity?

I am pretty intrigued by the record time that a qubit has survived.
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10 votes
3 answers
332 views

Can one interrogate black boxes for quantum coherence?

This question is based on a scenario that is partly hypothetical and partly based on the experimental features of molecule-based quantum devices, which often present a quantum evolution and have some ...
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10 votes
1 answer
293 views

What kinds of ions do trapped ion quantum computers use?

Trapped ion quantum computers are among the most promising approaches to achieve large-scale quantum computation. The general idea is to encode the qubits into the electronic states of each ion, and ...
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15 votes
3 answers
563 views

Scalability of ion trap quantum computers

My understanding is that the magnetic fields needed to hold the ions in place in ion trap quantum computers are very complex, and for that reason, currently, only 1-D computers are possible, therefore ...
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