Questions tagged [physical-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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38
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4answers
9k views

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 ...
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7answers
7k views

Why is it harder to build quantum computers than classical computers?

Is it because we don't know exactly how to create quantum computers (and how they must work), or do we know how to create it in theory, but don't have the tools to actually execute it in practice? Is ...
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2answers
6k 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 ...
23
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3answers
2k 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,...
21
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1answer
7k 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 ...
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3answers
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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 ...
18
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1answer
771 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?
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1answer
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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 ...
15
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2answers
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? ...
14
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3answers
431 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 ...
14
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2answers
1k 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 ...
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2answers
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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 ...
13
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662 views

How to store qubits while preserving Heisenberg's uncertainty principle?

I know that qubits are represented by quantum particles (for example photons) and that their state is given by one property (for example spin). My question is about the quantum memory: how are the ...
13
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1answer
475 views

How are quantum gates realised, in terms of the dynamic?

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 "...
12
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2answers
874 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 ...
11
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2answers
5k views

How many operations can a quantum computer perform per second?

I want to know what time complexity is considered efficient/inefficient for quantum computers. For this, I need to know how many operations a quantum computer can perform per second. Can anyone tell ...
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4answers
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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 ...
11
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1answer
207 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 ...
11
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1answer
344 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 ...
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3answers
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What countries are leading this “Global Quantum Computing Race”?

The terms Quantum Computing Race and Global Quantum Computing Race have been used in the press and research communities lately in an effort to describe countries making investments into a "battle" to ...
10
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2answers
527 views

What real quantum computers are available for students to use?

I am aware that IBM, Rigetti, and Google have built some small-scale devices. Which of them are available for access by an undergraduate student? For how long? With how many qubits?
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2answers
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Who built the first quantum computer using at least two qubits?

In my previous question I asked who invented a quantum computer using qubits. As a follow-up to this question I want to ask who built the first quantum computer using at least two qubits. During my ...
9
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2answers
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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,...
9
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3answers
473 views

Is it important for a quantum computer to be shielded by the magnetic field?

I've been browsing The D-Wave 2000Q site when I bumped into this aspect of their quantum computers: A Unique Processor Environment Shielded to 50,000× less than Earth’s magnetic field Why is that ...
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3answers
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What is D-Wave's “Pegasus” architecture?

How is D-Wave's Pegasus architecture different from the Chimera architecture?
9
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1answer
207 views

Current limits on Grover search space

I was wondering why till date Grover search has been implemented only till 3 qubits (corresponding to size of database = 8). Refer this paper The reason why I ask is that we have much larger sized ...
9
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3answers
326 views

What does it mean for a quantum computer to have $X$ qubits?

I want to preface with a disclaimer that I am a physicist with minimal knowledge of computer hardware. I have a solid understanding of quantum information from a theoretical standpoint but zero ...
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2answers
660 views

The process for transferring qubits between locations

I understand that right now qubits are physical entities in a Quantum Computer and I am playing around on the IBM Quantum Computer as well as the Q# language and dipping my toes into the Quantum world ...
8
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2answers
715 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 ...
8
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2answers
143 views

Dependency of architecture on hardware

How much of a role does the type of hardware used to implement the building blocks (like qubits, the circuits, the communication channels,quantum RAM etc.) have to play when designing the architecture ...
8
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2answers
223 views

Why attenuator and not filters for QC driving line

In all the cold quantum computer designs (superconducting qubits, spin qubits) attenuators are put on the driving lines. Their role is to kill the noise spectral density that comes from higher ...
7
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3answers
290 views

How to implement a while loop in a quantum computer?

How can a while loop be implemented in a quantum computer? If quantum computing consists of : preparing a state applying a unitary operator measuring, then it seems like it's not possible to wait ...
7
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2answers
419 views

How much faster is “D-Wave Two” compared to its predecessor?

I don't have any specific task or algorithm in mind, so depending on how they were tested – Is there any research which shows just how the D-Wave Two computer was faster (in terms of computation ...
7
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2answers
327 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 ...
7
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2answers
307 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?
7
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1answer
109 views

Does a fully working quantum computer solve a specific problem at varying speeds every time?

Lets say we have a fully working quantum computer. I give it a problem to solve and measure how long it takes to solve it. I repeat the process. Would it take the exact same time to solve the same ...
7
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0answers
148 views

What are the main obstacles to overcome to build silicon-photonic quantum computers?

In superconducting quantum computers, we use mostly superconducting qubits or trapped ions. However, those systems are quite large because their environment either requires near absolute zero ...
7
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3answers
655 views

When can we expect the first (universal) quantum computer being able to do something useful outside the academic world? [closed]

The governments, big companies (list of quantum processors) and smaller ones are in the competition of building bigger and bigger quantum computers. Not unexpectedly the number of qubits of those ...
6
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1answer
2k views

Why use U2 and U1 gate in IBM quantum computers?

I was wondering why IBM's computer were using U1 and U2 gates as part of there basis gates since as I understood, they are particular cases of the U3 gate. Why not just use U3 gate instead ? Thanks ...
6
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2answers
269 views

Are quantum simulators like Microsoft Q# actually using quantum mechanics in their chips?

Unlike Google's Bristlecone or IBM's Qbit computer, do simulators like Q# or Alibaba really use quantum mechanics anywhere in their physical chips? Are they just defining properties using a classical ...
6
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2answers
758 views

What are examples of quantum computing platforms availble for free (other than IBM Q)?

IBM Q is (maybe first) quantum computing platform allowing users to register for free and run algorithm on real quantum processors. There are several processors with usually 5 qubits, however, it is ...
6
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2answers
227 views

Can quantum computers design quantum computers autonomously better than other methods?

We've seen people use computers to design computers, AI to write computer programs, robots teach themselves, and even robots build themselves. I understand that conventional computers can be used to ...
6
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1answer
848 views

Is there any single-logical-qubit physical device out there as of end 2018?

By my first impression, there are many-qubits computers out there and more to come, as to follow the press. Now a closer look reveals that it's all about designing and building physical qubits. ...
6
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1answer
280 views

Physical qubit of optical quantum computer

I was researching how optical quantum computers work and discovered a KLM protocol that allows for building quantum gates using linear optics elements like mirrors, beam splitters, and phase shifters. ...
6
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2answers
385 views

Randomness from deterministic machine

It is known that in a classical computer we can't generate a purely random number by deterministic process. I am taking a course in Quantum Computing, recently I learnt that using state we can ...
6
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1answer
176 views

Do the latest D-Wave computers use Helium compounds for cooling?

Do the latest D-Wave machines use compounds of $\require{\mhchem}\ce{^{3}He}$ and $\ce{^{4}He}$ for cooling? If not, how does D-Wave approach cooling its plates low enough to achieve superconductivity?...
6
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1answer
122 views

Claimed “potential revenue” from machine learning in 2023?

In this plot: taken from here, IonQ is claiming to have a potential application in machine learning by 2023. What applications could they have in mind? From what I understand, modern error correction ...
6
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1answer
91 views

How scalable are quantum computers when measurement operations are considered?

From a high-level point of view, given a quantum program, typically the last few operations are measurements. In most cases, in order to extract a useful answer, it is necessary to run multiple ...
6
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1answer
227 views

Does this experimental discovery of anyons enables the topological quantum computer (e.g. Microsoft) to become a reality?

Microsoft has its own agenda regarding quantum computer - it is topological quantum computer being invented by the team lead by Michael Freedman https://www.microsoft.com/en-us/research/project/...
6
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1answer
374 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 ...