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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 quantum computers seem to double every year but those qubits are noisy qubits. What is a more meaningful metric is the number of error corrected qubits and some sources say that we need 100 noisy qubits to simulate one error corrected qubit.

Besides the error corrected qubits there are other substantial hurdles that need to be passed to come to a universal quantum computer that can do something useful (see Why Will Quantum Computers be Slow?)

I read quotes like (source GOOGLE, ALIBABA SPAR OVER TIMELINE FOR 'QUANTUM SUPREMACY):

Intel CTO Mike Mayberry told WIRED this week that he sees broad commercialization of the technology as a 10-year project. IBM has said it can be “mainstream” in five.

So when might we actually expect the first universal quantum computer that can do something useful outside the academic world ?

With useful I mean that brings real value (e.g. commercial application) and that cannot be done with same efficiency using existing classical computing algorithms/models.

I have deliberately mentioned outside the academic world as obviously currently pure by their existence the current quantum computers are useful for the theoretical computer scientist, quantum physicist, quantum specialist, ...

What currently interests me more is the usefulness of the outcome of this quantum algorithm for real world problems (e.g. cracking an actual key, designing a new molecule with specific characteristics, finding the optimal solution of an actual problem, recognizing real images, ....)

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closed as primarily opinion-based by MEE the setup wizard, Niel de Beaudrap, Discrete lizard, glS, Mithrandir24601 Jun 22 '18 at 11:01

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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2028

[1] Source Scientific American : How Close Are We—Really—to Building a Quantum Computer?(Intel’s head of quantum computing talks about the challenges of developing algorithms, software programs and other necessities for a technology that doesn’t yet exist)

The race is on to build the world’s first meaningful quantum computer—one that can deliver the technology’s long-promised ability to help scientists do things like develop miraculous new materials, encrypt data with near-perfect security and accurately predict how Earth’s climate will change. Such a machine is likely more than a decade away, but IBM, Microsoft, Google, Intel and other tech heavyweights breathlessly tout each tiny, incremental step along the way.

and a bit further down the same article:

People think quantum computers are just around the corner, but history shows these advances take time. If 10 years from now we have a quantum computer that has a few thousand qubits, that would certainly change the world in the same way the first microprocessor did. We and others have been saying it’s 10 years away. Some are saying it’s just three years away, and I would argue that they don’t have an understanding of how complex the technology is.

[2] Source : When Will Quantum Computers Be Consumer Products?

Andrew Dzurak, Professor in Nanoelectronics at University of New South Wales, ... “I think that within ten years, there will be demonstrations of modelling of certain chemicals and drugs that couldn’t be done today but I don’t think there will be a convenient, routine [system] that [people] can use,” Dzurak said in the interview. “To move to that stage will take another decade further beyond that.”

[3] Why Quantum Computing Should Be on Your Radar Now

This report could also be interpreted that the first useful thing could happen earlier than 2028 (e.g. in 2023)

What to expect, when

There's a lot of confusion about the current state of quantum computing which industry research firms Boston Consulting Group (BCG) and Forrester are attempting to clarify.

In the Forrester report, Hopkins estimates that quantum computing is in the early stages of commercialization, a stage that will persist through 2025 to 2030. The growth stage will begin at the end of that period and continue through the end of the forecast period which is 2050.

...

BCG also reasons that the quantum computing market will advance in three distinct phases:

  1. The first generation will be specific to applications that are quantum in nature, similar to what D-Wave is doing.

  2. The second generation will unlock what report co-author and BCG senior partner Massimo Russo calls "more interesting use cases."

  3. In the third generation, quantum computers will have achieved the number of logical qubits required to achieve Quantum Supremacy. (Note: Quantum Supremacy and logical qubits versus physical qubits are important concepts addressed below.)

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2033 or later

[1] source Why will quantum computers be slow?

This site mentions the following bottlenecks:

  1. Bottleneck #0: Qubit count
  2. Bottleneck #1: T count
  3. Bottleneck #2: Measurement depth
  4. Bottleneck #3: Spacetime volume

Regarding the first bottleneck it says the following:

If the qubit count doubles every year, it'll be 17 years before we get to 100%. That 17 year gap is daunting. 50 to 100 noisy qubits should be enough to do something hard, and 100 to 200 logical qubits should be enough to do something useful, but at the moment it's not known if there's much in between. If there really is nothing on the decade-long road from 100 noisy qubits to 100 error-corrected qubits,

The summary of the blog:

Summary To run a quantum computation really fast, you need:

1 Enough qubits to fit the computation in the first place. 2 Then enough T factories to perform T gates as fast as the computation needs them. 3 Then wider circuits that do measurements in parallel instead of serially. 4 Then efficient strategies for routing qubits and packing braiding operations.

I like to imagine that each bottleneck will be the "most relevant" for about a decade. We'll naturally transition from one to the next because, funnily enough, every single one of these bottlenecks falls to adding more qubits....

[2] The points mentioned in answer 2028 mainly give an indication when they expect it might happen. They are not excluding it can be several years later.

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2023

[1] Source IBM Research https://www.research.ibm.com/5-in-5/quantum-computing/

... Within five years, the industry will have discovered the first applications where a quantum computer (used alongside a classical computer) will offer a benefit to solving specific problems. ...

[2] point [3] in answer 2028 also supports to some extent this period.

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