Quantum Computing in Practice: The Challenges to Overcome to Turn Theory into Reality

On Engadget I have spoken of what is probably the future of computing: the quantum computing. We have seen as the superposition of States and interlacing allows us to make multiple simultaneous operations on a single qubit, which is what gives to quantum computing the exponential power.

Now, this is only theory. How we carry everything in practice? How to make a device capad measure and modify quantum States? What can we achieve with quantum computers? These are not trivial questions. In this article we will see what are those current challenges of quantum computing… notamargen {float: right; margin-left:-250px! important; position: relative; left: 280px; width: 250px; font-style: italic; font-size: small;}

What we use for the qubits?

In the traditional computing, electricity is what represents the bits. There is still not a definitive equivalent to quantum computing. Image source.

The first question is What we take to represent the qubits. So far we have only spoken of them as things abstract, mathematical objects that can be in several States. In practice, we need to choose a particle or element physically represent this qubit, in the same way as in traditional computer bits are represented by a cable through which it passes or not electricity.

The decision is not easy. If we want to observe the quantum effects we need small, such as molecules, atoms or electrons physical systems. But manipulating those elements is not easy, nor is it accurate measurements of its States.

There are many possibilities that scientists have been exploring to implement quantum computers. One of which has had more success has been the nuclear magnetic resonance (MRI), mainly because it is a technology already ripe with which it is relatively easy to implement a computer.

In fact, it was with an NMR computer that ran for the first time in 2001 of Shor quantum algorithm for factoring numbers. But like everything else in nature, ease hand comes with difficulties on the other.

With NMR quantum computing is based on measuring the States of spin of certain atoms in a molecule. For example, the spin of the atoms of carbon is sometimes used in the molecule of alanine, which you have in the picture. As there are three atoms of carbon (black), we have a system of three qubits.

As you can imagine, this technique does not help us much for multiple qubits. The problem is that there are many interferences in large molecules that are going to alter the qubits without we realize, and the computations we do will be wrong. It is the phenomenon of the noise, and one of the biggest challenges to overcome in quantum computing.

To the scale at which quantum effects occur, the noise is a serious and complicated to solve problem.

The noise can reach even to deinterlace the particles in a short time, so that in a poorly insulated system not only we would have a wrong qubit from time to time, but calculations that if it takes longer than one certain time cease to be valid. The issue is complex since the noise can come from the elements themselves used as qubits, fluctuations that do end up changing its state when they should remain stable.

D-Wave, computers with superconducting circuits

Where more progress has been made is in the representation of qubits with superconducting circuits. Depending on the type of circuit, what is measured is the load or the direction in which the electrons move in a loop. So there is no loss or fluctuations due to temperature (which we mentioned before the noise), must be cooling circuits to a point very close to absolute zero (-273 °).

DWave, superconducting circuits-based processor.

With this technology, in D-Wave have succeeded in creating the first quantum processors ‘commercial’, with practical applications real (in Google have one, for example). The problem is that need to cool down so much, it seems difficult to create a small processor based on the same idea.

Scientists are still investigating possibilities at its disposal to create a manageable and universal quantum computer. But There is one problem more.

Are you sure that’s a quantum computer?

It sounds weird, but not all computers made with qubits are quantum. If we recall the theory, what was special to quantum computing is the interlacing, the fact that the States of two particles are strongly related. With that we got to that, with n particles had 2n States, and it was that gave the exponential power to quantum computers. Interlacing is what makes the difference.

It is difficult to know if there is or not interlacing in a quantum computer.

Well, it turns out that many supposedly quantum computers, has not observed this phenomenon with security. For example, in one of the most advanced quantum processors, the D-Wave Two, It failed to measure the improvement of theoretical speed that should be.

Of course, that does not rule out entirely that the computer is quantum. Know if particles are intertwined or is not difficult, and it is the other challenge of quantum computing.

And now that I have a quantum computer, what should I do?

In Engadget we have already spoken of some progress made with quantum computers, as for example Google using one to help Google Glass. However, on Engadget mentioned that program to a quantum computer is very different to do so for a normal computer. Clarify: what you can do right now with a quantum computer?

Artificial intelligence and machine learning are the main beneficiaries of quantum computing.

The truth is that There are many algorithms quantum that they exploit all the possibilities of computers of this type. One of them and has allowed major advances in machine learning.

This field of the artificial intelligence, very glamorous as it may sound, actually is rather crude. Most of those systems so advanced and intelligent, able to recognize faces or understand phrases, have actually been generated “randomly”: creates a function with certain parameters, is regarded as often fails, parameters are modified, and repeat the process, until at the end, you end up with something that seems to work.

It turns out that quantum computers can solve easily that kind of optimization problems with the algorithm of temple, which roughly consists of putting the qubits in a given State (initial parameters of the function) and wait, by applying a constant disturbance. In the end, the qubits reach some parameters that, with high probability, minimize the number of errors.

Analog in the real world would be throwing a marble down a Hill: always tends to go a point lower. However you just have to give him a kick from time to time to make sure that it is not at intermediate points. That kick would be the equivalent to the phenomenon of “quantum tunnel”, consisting of a simplified move from one State to another, although there is a seemingly impossible jump “barrier” between stockings.

Teaching a computer

The quantum temple is like throwing a marble on a Hill: goes to the point lower. Could a quantum computer decide what is the best dose of radiation for a cancer-fighting (e.g. simplified, obviously).

In other words: an application of quantum computers is to create faster and more accurate machine learning systems that that can be created with traditional computers.

And what we use machine learning? For many processes that we are not able to recreate on a computer. For example, automatic learning systems can be used to find out what is the best way to apply radiation to a patient, to detect objects in images, or to create statistical models that predict the evolution of the stock market. In general, are used for processes that we are not able to exactly model (nobody knows to explain to a computer what exactly is a smile, to take a silly example) but for those who have a lot of data that the computer can be used to learn.

D-Wave Two, the second commercial quantum processor, is made for solving optimization problems. Google and NASA have one to investigate its applications in artificial intelligence.

The theory says that quantum computing could also be applied to other fields, such as the of the Security. As we mentioned in Engadget, there is a quantum algorithm designed for factoring numbers quickly, which would leave to RSA in a joke and would break much of Internet security. However, still not have been to create computers with sufficient capacity to do this.

What it the future hold?

That’s a good question. Although there is progress (D-Wave is the company with the head with its Two D-Wave, a processor of 512 qubits), we are still in a phase very, very early. As we said before, we don’t even know if the computers are actually quantum. There is evidence and indeed the D-Wave systems are faster than the computer you may have in your home, but still not they clearly surpass all classic computers in all situations, which is what would be expected.

One of the fields that would be most affected by the advancement of quantum computing would be the of the Cryptography. Public key systems are based on problems as of the factorization of integers, problems that solve a classical computer in years. But, as we mentioned before, a quantum computer could solve it in a time much smaller and break as well the security of many systems of Internet, such as HTTPS. Luckily, there are advances in what is called post-cuantica cryptography, secure systems even with quantum computers.

Whatever it is, We still have much time until quantum computing reaches a minimum point of maturity, and a lot more so that it becomes a technology so widespread as computing today, if it is that at some point it gets.