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Questions tagged [experimental-realization]

For questions about physical implementations of a quantum algorithm or other quantum information protocol. DO NOT use for questions about simulation or emulation of quantum computers, or cloud-based quantum computing services like the IBM Q Experience.

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How do I add 1+1 using a quantum computer?

This can be seen as the software complement to How does a quantum computer do basic math at the hardware level? The question was asked by a member of the audience at the 4th network of the Spanish ...
agaitaarino's user avatar
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16 votes
1 answer
3k views

What is the physical representation of a qubit?

In regular computers, bits may be physically represented using a wide variety of two-state devices, such as polarity of magnetization of a certain area of a ferromagnetic film or two levels of ...
user avatar
8 votes
0 answers
368 views

In D-Wave's universal quantum computer, why does the YY term have to be driven along with the linear X term?

D-Wave has a new prototype annealer that uses a Hamiltonian which, if there was enough qubits and sufficient control, would be able to simulate any universal circuit-based quantum computer with at ...
user1271772 No more free time's user avatar
50 votes
2 answers
7k views

Is there proof that the D-wave (one) is a quantum computer and is effective?

I'm admittedly a novice in this field, but I have read that, while the D-wave (one) is an interesting device, there is some skepticism regarding it being 1) useful and 2) actually a 'quantum computer'....
Discrete lizard's user avatar
20 votes
6 answers
2k views

What is a qubit?

What is a "qubit"? Google tells me that it's another term for a "quantum bit". What is a "quantum bit" physically? How is it "quantum"? What purpose does it serve in quantum computing? Note: I'd ...
Mithical's user avatar
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9 votes
2 answers
435 views

Are we certain that quantum computers are more efficient than classical computers can be built?

I mean are we certain that they will be able to provide us a huge improvements (in some tasks) compared to clasical computers?
Adou's user avatar
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8 votes
2 answers
651 views

What's the difference between a set of qubits and a capacitor with a subdivided plate?

This is probably just a misunderstanding on my part, but everything I've seen on what quantum computers do thus far seems to suggest that the actual process of reading the entangled qubits would be ...
CoryG's user avatar
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8 votes
1 answer
2k views

Physical implementation of gates on IBM Q

There is a lot of quantum gates in IBM Q Composer, however, only few are implemented physically while others can be composed of them. When one looks at description of a quantum processor in IBM Q ...
Martin Vesely's user avatar
44 votes
3 answers
10k views

How does a quantum computer do basic math at the hardware level?

On reading this Reddit thread I realized that even after a couple months of learning about quantum computing I've absolutely no clue about how a quantum computer actually works. To make the question ...
Sanchayan Dutta's user avatar
36 votes
1 answer
14k views

How are quantum gates implemented in reality?

Quantum gates seem to be like black boxes. Although we know what kind of operation they will perform, we don't know if it's actually possible to implement in reality (or, do we?). In classical ...
Sanchayan Dutta's user avatar
25 votes
3 answers
3k views

Why do optical quantum computers not have to be kept near absolute zero while superconducting quantum computers do?

This is a follow-up question to @heather's answer to the question : Why must quantum computers be kept near absolute zero? What I know: Superconducting quantum computing: It is an implementation of ...
Sanchayan Dutta's user avatar
25 votes
2 answers
703 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 No more free time's user avatar
21 votes
1 answer
12k views

What is the difference between a qubit and classical bit?

As I understand it, the main difference between quantum and non-quantum computers is that quantum computers use qubits while non-quantum computers use (classical) bits. What is the difference between ...
luap42's user avatar
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14 votes
2 answers
4k views

Is Google's 72 qubit device better than D-Wave's machines, which feature more than 2000 qubits? [duplicate]

Google recently announced the Bristlecone 72 qubit quantum computer. However, D-Wave already announced quantum computers featuring more than $2000$ qubits. Why is Google's new device newsworthy then? ...
Devansh Sharma 's user avatar
9 votes
2 answers
846 views

How to explain in layman’s terms the significance of the difference of qubits of the D-Wave and IBM QX?

So, @AndrewO mentioned recently that he has had 'encounters' with people wondering why D-Wave has a lot more qubits than IBM. Of course, this comparison is faulty, since the IBM and D-Wave's machine ...
Discrete lizard's user avatar
6 votes
3 answers
3k views

Why can't we simulate a Qubit using classical computer?

I am completely a noob in terms of quantum computing, have watched several videos to understand what Quantum computers are trying to achieve. I am a programmer of classical computers. We have a ...
Anurag Vohra's user avatar
5 votes
2 answers
395 views

Is it possible to have access to real quantum computers that have more than 15 qubits for my master thesis?

My physics master thesis is about variational quantum optimization and I have to run algorithms with more qubits than 15. Is it possible to make any requests to use larger IBM real quantum computers?
Antonio Anna Mele's user avatar
25 votes
3 answers
3k views

What is the argument that practical quantum computers cannot be built?

An answer to another question mentions that There are arguments that suggests that such machines ["quantum Turing machines"] cannot even be built... I'm not sure I fully understand the problem,...
BurnsBA's user avatar
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19 votes
2 answers
466 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 ...
agaitaarino's user avatar
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19 votes
3 answers
11k views

What does it mean for two qubits to be entangled?

I have done some sort of online research on qubits and the factors making them infamous i.e allowing qubits to hold 1 and 0 at the same time and another is that qubits can be entangled somehow so that ...
Arshdeep Singh's user avatar
17 votes
2 answers
3k views

Why must quantum computers be kept near absolute zero?

Online descriptions of quantum computers often discuss how they must be kept near absolute zero $\left(0~\mathrm{K}~\text{or}~-273.15~{\left. {}^{\circ}\mathrm{C} \right.}\right)$. Questions: Why ...
Didix's user avatar
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14 votes
3 answers
1k 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.
Daniel Tordera's user avatar
13 votes
2 answers
1k views

Is the "Quantum Volume" a fair metric for future, elaborate, high value quantum computations?

A metric called the "quantum volume" has been proposed to somehow compare the utility of different quantum computing hardware. Roughly speaking, it measures their worth by the square of the maximum ...
user avatar
13 votes
6 answers
2k views

Resources for quantum algorithm basics

I have just started to learn about quantum computing, and I know a little bit about qubits. What is a resource where I can learn a basic quantum algorithm and the concepts behind how it works?
Vashi's user avatar
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12 votes
2 answers
689 views

How are elementary quantum gates realised?

When expressing computations in terms of a quantum circuit, one makes use of gates, that is, (typically) unitary evolutions. In some sense, these are rather mysterious objects, in that they perform "...
glS's user avatar
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10 votes
4 answers
2k views

Do real commercial quantum computers exist?

We have been reading about quantum computers being developed and tested in labs. And also, we have quantum simulator programs that use limited virtual qubits (up to 30-40 qubits if cloud-based). And ...
Koder101's user avatar
  • 997
10 votes
4 answers
692 views

Is there any company that backs and implements diamond vacancy quantum computers?

It is known that there are big companies behind the specific qubit implementations (e.g. ion traps, superconducting loops, topological qubits, etc.). But I have not managed to find the company that is ...
TomR's user avatar
  • 413
7 votes
1 answer
189 views

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: ...
agaitaarino's user avatar
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6 votes
1 answer
1k views

What is the state of the art on Quantum Random Access Memories? [duplicate]

I realized that Quantum Random Access Memory (qRAM) was proposed to make quantum computers more similar to classical one. Currently quantum computers have very constrained memory, given only quantum ...
Martin Vesely's user avatar
6 votes
3 answers
2k views

Is there anything practical that can be done with a single qubit?

Is there anything practical that can be done with a single qubit? And by "practical," I mean a problem that can be solved or information that can be stored. I realize that one practical thing that ...
vy32's user avatar
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5 votes
1 answer
319 views

Do we really know how a universal quantum computer can be used to revolutionize the design of new drugs or materials?

One of the most promising applications of a quantum computing is the design of new drugs and materials: Quantum computers promise to run calculations far beyond the reach of any conventional ...
JanVdA's user avatar
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3 votes
1 answer
58 views

Fisher information from likelihood function for discrete quantum case

In the context of a single phase estimation problem of a quantum photonics experiment. For example consider a 3-photon quantum circuit (such as the Mach-Zehnder which depends on some phase shift ...
John Doe's user avatar
  • 901
3 votes
1 answer
291 views

Where are the physical gates in the Google processor?

Google's article Quantum supremacy using a programmable superconducting processor states that the processor "53 qubits, 1,113 single-qubit gates, 430 two-qubit gates, and a measurement on each qubit, ...
vy32's user avatar
  • 641
20 votes
1 answer
1k views

What cryogenic systems are suitable for superconducting qubits?

Is a dilution refrigerator the only way to cool superconducting qubits down to 10 millikelvin? If not, what other methods are there, and why is dilution refrigeration the primary method?
auden's user avatar
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18 votes
1 answer
4k views

Which subatomic particle does each company use in quantum computing?

Probably each company (Google, Amazon, Intel, IBM, Microsoft, D-Wave and so on) uses a mix of subatomic particles and technologies. I would like to know which particles/technologies are used by each ...
Felipe Rojo Amadeo's user avatar
14 votes
2 answers
3k views

How power-efficient are quantum computers?

Quantum algorithms scale faster than classical ones (at least for certain problem clases), meaning quantum computers would require a much smaller number of logical operations for inputs above a given ...
Alex Jone's user avatar
  • 633
11 votes
1 answer
435 views

Does the D-Wave 2000Q satisfy DiVincenzo's criteria?

DiVincenzo's criteria for quantum computation are the following: A scalable physical system with well characterized qubits. The ability to initialize the state of the qubits to a simple fiducial ...
user1271772 No more free time's user avatar
10 votes
1 answer
725 views

How do you apply a CNOT on polarization qubits?

I read that a qubit can be encoded in a polarization state (horizontal or vertical polarization of a photon). How do you perform two-qubit operations on a polarization qubit?
Daniel Tordera's user avatar
10 votes
3 answers
389 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 ...
agaitaarino's user avatar
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10 votes
2 answers
2k views

What is the difference between a qubit and a quantum state?

In general, a qubit is mathematically represented as a quantum state of the form $\lvert \psi\rangle = \alpha \lvert 0\rangle + \beta \lvert 1\rangle$, using the basis $\{ \lvert 0\rangle, \lvert 1\...
user avatar
9 votes
2 answers
2k views

Allowed CNOT gates for IBM Q 5 quantum computer

I trying to do some tests in the IBM Q5 computer of IBM quantm experience for some simple error correction protocols, but as I can see, some operations between the qubits are not allowed. For example,...
Josu Etxezarreta Martinez's user avatar
9 votes
3 answers
2k views

What is D-Wave's "Pegasus" architecture?

How is D-Wave's Pegasus architecture different from the Chimera architecture?
user1271772 No more free time's user avatar
8 votes
2 answers
570 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. ...
SalvaCardona's user avatar
8 votes
2 answers
174 views

How to interpret $-\rvert1\rangle \otimes \rvert1\rangle = -\rvert11\rangle$?

I'm having trouble accepting, intuitively, that $-\rvert1\rangle \otimes \rvert1\rangle = -\rvert11\rangle = \rvert1\rangle \otimes -\rvert1\rangle$. It's my understanding that $ -\rvert1\rangle$ ...
Dragonsheep's user avatar
8 votes
4 answers
2k views

Non-layperson explanation of why a qubit is more useful than a bit?

I have a computer science and mathematics degree and am trying to wrap my head around quantum computing and it just doesn't seem to make sense from the very beginning. I think the problem is the ...
Lee Cascio's user avatar
7 votes
2 answers
212 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
  • 3,302
7 votes
2 answers
3k views

What are the pros/cons of Trapped Ion Qubits, Superconducting Qubits and Si Spin Qubits?

Among available qubit technologies for universal quantum computing these 3 come up as promising. NV centers and Majorana qubits also underway but relatively new. I find superconducting qubits and ...
mando's user avatar
  • 355
7 votes
1 answer
3k views

How does the CNOT gate operate when the control qubit is a superposition?

If a control qubit is in superposition, how it will affect target qubit if it is collapsed or in superposition? Is it true that CNOT works only if the control bit collapsed to 1? Also, is it possible ...
Olexander Korenyuk's user avatar
7 votes
3 answers
666 views

Does Google's error correction paper invalidate Gil Kalai's arguments?

In his paper "The Argument against Quantum Computers, the Quantum Laws of Nature, and Google’s Supremacy Claims", Gil Kalai argues that quantum advantage will never be reached. For NISQ ...
Tristan Nemoz's user avatar
  • 6,162
7 votes
1 answer
354 views

Are there measuring standards (and units) for the identification of qubits?

The representation of bits in different technological areas: Normal digital bits are mere abstractions of the underlying electric current through wires. Different standards, like CMOS or TTL, assign ...
AG-M's user avatar
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