Questions tagged [physical-realization]

For questions about practical computers or processors that run on a quantum architecture. This is for questions about the machines themselves, not just any computing that could take place on one. You may also use this tag for questions on realistic implementations of quantum channels. 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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33
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4answers
6k 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
5k 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
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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,...
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3answers
2k 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 ...
19
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1answer
639 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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3k 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? ...
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1answer
5k 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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2answers
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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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363 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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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 ...
12
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2answers
581 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 ...
12
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1answer
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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 "...
11
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2answers
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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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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 ...
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495 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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How power-efficient are quantum computers?

As we all know, 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 ...
11
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1answer
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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 ...
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778 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 ...
10
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2answers
268 views

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 ...
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3answers
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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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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,...
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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
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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 ...
9
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1answer
160 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 ...
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3answers
283 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
398 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 ...
8
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2answers
522 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
132 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 ...
7
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2answers
618 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 ...
7
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1answer
102 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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2answers
244 views

Are we certain that quantum computers 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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3answers
587 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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3answers
138 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 ...
6
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2answers
257 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
197 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
199 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
276 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
89 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
103 views

Is there any legitimate information about Microsoft quantum hardware?

I'm wondering if anyone has information regarding the current status of Microsoft quantum hardware? How many working qubits do they have? What are the gate depth/fidelity? Any details about ...
6
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1answer
395 views

Transmons and cooper pair box qubits: two islands or a single island and a reservoir

In scientific literature, one typically describes Cooper pair boxes as a small superconducting island coupled to a superconducting reservoir (say, a large ground plane of superconducting metal, or a ...
6
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0answers
110 views

Calculating power of a quantum computer — RSA

As discussed in this question, the expected security of 1024-bit RSA is 80-bits: NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength ...
6
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0answers
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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 ...
5
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2answers
695 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 ...
5
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1answer
829 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. ...
5
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1answer
224 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 ...
5
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1answer
168 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?...
5
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2answers
64 views

What are some good resources for learning about photonic qubits?

I am interested in resources that would allow me to learn about the physics behind optical quantum computation, and specifically, the physical properties of photonic qubits. I have some good resources ...
5
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1answer
114 views

Why are multiple quantum gates, in a quantum circuit, used?

After reading about quantum computers, for a high school research paper, a few questions arose concerning quantum logic gates. At first, it seems that quantum logic gates are in essence various ...