
Rigetti launches the public beta of its Quantum Cloud Services - sahin-boydas
https://techcrunch.com/2019/01/30/rigetti-launches-the-public-beta-of-its-quantum-cloud-services/
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krastanov
This is exciting! But keep in mind that the PR materials can be confusing. If
you look at the specs
[https://www.rigetti.com/qpu](https://www.rigetti.com/qpu) you can see their
quantum processors have on the order of 10 qubits, and after less than ~10
logical gates the state of the system will be completely scrambled due to the
imperfections of the gates. It is a great milestone, and it should be
celebrated, but we need something much bigger and way less sensitive to noise
to be able to call it "quantum computer".

~~~
voiper1
How many qubits for useful quantum calculations? What are use cases for
quantum computing, that it gives an advantage over regular CPU/GPUs?

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krastanov
The advantage of scalable digital quantum computers when/if they get built is
that they can do certain very specific mathematical operations in polynomial
time (instead of exponential for classical computers). This is a fairly
imprecise statement (but gives good intuition). It is conjectured without yet
being proven (still, there are many clues to it being true). It applies only
to very specific problems, so there are "classically easy" problems which we
will just continue solving with classical computers, and there are many
problems that are infeasibly difficult for both classical and quantum
computers.

An example of where quantum computers will excel is simulating large organic
molecules (which is impossible today) ushering a new era of drug discovery and
material science.

While there are toy applications of small computers, you probably need
hundreds or thousands logical qubits. Given the low quality of the hardware
and the environmental noise it is expected that you will need to use error
correction codes where you encode a single logical qubit on top of hundreds or
thousands of physical qubits.

In other words, once we have a machine with 10000 physical qubits that can all
be well controlled and entangled with each other, with gate fidelities of 0.99
nobody (almost nobody) will be able to argue that it is not a quantum
computer.

This device here has 20ish qubits with gate fidelities of 0.8 to 0.98.

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phoe-krk
Shameless smuglispweeniesm: Rigetti is one of the companies using Common Lisp
in their research and development.

[https://www.youtube.com/watch?v=f9vRcSAneiw](https://www.youtube.com/watch?v=f9vRcSAneiw)

~~~
reikonomusha
Not just R&D, but it runs in production as well. Their downloadable SDK as
well as some of the software backing their QMI’s are written in Lisp.

~~~
jxy
Which CL implementation do they use in production?

~~~
phoe-krk
Scanning their GitHub repositories shows that they are written for SBCL.

[0] [https://github.com/rigetti/rpcq](https://github.com/rigetti/rpcq)

[1] [https://github.com/rigetti/magicl](https://github.com/rigetti/magicl)

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muhneesh
Congratulations to the team.

If anyone's reading this, what are you expecting in terms of outcomes from the
public beta?

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kkaranth
As someone who understands nothing about quantum computing, what are some good
resources to begin learning? Hopefully with examples/code that I can run.

~~~
learned
Yanofsky and Manucci's "Quantum Computing for Computer Scientists" is a smooth
intro if you come from a CS background.

Nielsen and Chuang's "Quantum Computation and Quantum Information" is more
thorough and advanced from a mathematical point of view. But it contains a
primer on the linear algebra required.

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matt2000
Does anyone know where this system stands performance wise vs classical
computers? Are there types of problems where this is known to be faster now?
Or are we still waiting for more qubits for that to happen? Thanks!

~~~
rsln-s
> Are there types of problems where this is known to be faster now?

Not yet. This is commonly called "quantum advantage" or "quantum supremacy",
i.e. proof that on a certain (even artificial and with no practical
applications) problem a quantum computer can perform better than classical
state-of-the-art. So far even for the task of simulating quantum circuits
(which quantum computer should definitely be better at!) we don't have enough
cubits to have a go at quantum advantage.

Depending on connectivity (full connectivity like on ionQ vs planar
connectivity like IBM / Rigetti), we need between 100-200 and thousands of
qubits to show quantum advantage (denser connectivity -> lower qubit number
requirement). And that's just for a synthetic problem with no applications.

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hannob
Of course none of that makes any sense.

No Quantum computer has been shown to do anything useful faster than a normal
computer. Everything you can do on any existing quantum computer you can do
faster on a normal computer.

If you want to play with quantum algorithms your best shot is simulating a
quantum computer.

Don't get me wrong: Scientists should do research on Quantum computers. They
may or may not be useful in the future. But selling QC as a (useful) service?
It's decades away.

