Digit Geek
Digit Geek > Recent Articles > Science > Lasers could give us room temperature quantum computers

Lasers could give us room temperature quantum computers

Laser, meet quantum computing

Quantum computing, and the work towards realising it has been around for ages now. Rather than boring you with the milestones that got it where it is today, it suffices to say that it is here. As Isaac Chuang, a lean, soft-spoken MIT professor, puts it “Quantum computing is no longer a physicist’s dream, it is an engineer’s nightmare”. We’ve had a slew of announcements from companies such as IBM, Google and Intel, each touting their own success, at whatever scale, into breaking the next barrier in quantum computing. Yet, at a macro level, it is evident that we are far from ‘quantum supremacy’ in practicality. Quantum supremacy, in this context, refers to the situation where quantum computers can actually achieve persistent results faster than a conventional computer. If the findings of a recent research paper are to be believed though, things could turn around pretty soon.

What it achieved

A computer works in terms of operations on 1s and 0s. A typical computer in 2018 can perform 1 billion of these operations per second. Thanks to the efforts of a group of researchers from Germany and the USA, computing in the near future might leave that number in the dust.

A lattice representation of WSe2 (Tungsten diselenide)

The experiment conducted involves pulsing infrared light on honeycomb-shaped lattices of tungsten and selenium. This allows the silicon bits to switch between 1 and 0 pretty much like a normal computer – only a million times faster. How does that happen? For that, we need to understand how electrons behave in a honeycomb lattice.

The principle

When it comes to molecules, electrons are usually in orbit around them in fixed quantum states. They can jump between these states/orbits/tracks as and when they gain or lose energy. These tracks are known as valleys by the researchers and the manipulation of these states as ‘valleytronics’.

In the tungsten-selenium lattice, only two tracks are available for electrons to burn off their excess energy. So, when you direct infrared light in a particular orientation at the lattice, you’ll excite an electron to move to the first track. Infrared light in a different orientation will excite the electron to move onto the second track. Now, when you think of these tracks as the states of a bit, i.e 1 and 0, you can see how this process can be used for computing.

Google’s Bristlecone can handle 72 qubits

But using them for this purpose isn’t exactly easy. That is because these electrons don’t really like hanging around on these tracks for too long. And they don’t need to. It only takes them a few femtoseconds to lose the excess energy and return back to the fixed tracks closer to the nucleus. To put the time period into perspective, the fastest thing in the universe, light, takes more than a femtosecond to cross a single red blood cell. So, how does this phenomenon even matter for computing? It does when successive beams of light can knock them back and forth between the two excited tracks, effectively creating a string of 1s and 0s in spectacularly quick flashes.

How it works

We’ve reached a point where quantum computers in laboratories around the world are working with 50 or more qubits. Earlier this year, in March 2018, Google announced a quantum computer with 72 qubits! That is well beyond what the most powerful traditional computer can simulate, which could be used to insinuate that humans have already achieved quantum supremacy. Yet, we have not seen any celebratory announcements or declarations from the quantum computing community yet. Why would that be?

2D conceptual chart showing the relationship between error rate and number of qubits. The intended research direction of Google’s Quantum AI Lab is shown in red

That is because quantum computing’s basic units, the qubits, are notoriously difficult to maintain. As we mentioned earlier, electrons aren’t exactly keen on maintaining a particular state for too long. Even with Google’s latest quantum computing platform Bristlecone, quantum computers need to be kept extremely cold and physically stable to avoid errors. To put a parameter on it, a quantum computer needs to have an error rate of less than 0.5 per cent for every two qubits to be useful in even remotely real-world scenarios. The best Google has achieved so far is 0.6 per cent with their 9 qubits linear array. And we’re speculating about 72 qubits here which is definitely an insurmountable barrier in the near future.

IBM’s 50 qubit system

The results achieved with the tungsten-selenium lattice could be the solution. These results have been achieved in room temperature conditions and the researchers have speculated that the same could be put to use for quantum computing. This is because this approach differs from trying to hold on to a quantum state for longer – it essentially tries to increase the amount of processing that can be done during the same amount of time, akin to increasing the clock speed on traditional computers. This can be done due to the ultrashort pulses of light that can be supplied.

These extremely short, configurable bursts of light were demonstrated almost a year ago by researchers, including engineers from the University of Michigan. They showed that the peaks within the laser could be controlled and could also be twisted, hence their ability to affect the quantum state of the electron differently each time they are used to excite it. The world of physicists would call this ‘lightwave electronics’.

Along with the two distinct states before and after the excitation, the electrons can also occupy superposition states where they hold both values 1 and 0 at the same time. Additionally, once energy is supplied, the electrons are constantly emitting light, making it easier to read the qubit without disturbing the already fragile quantum state.

The significance

Even though the current results hardly venture into actual quantum computing, in theory , they do work for the area. The researchers have successfully demonstrated this operation with one qubit and the next logical step would involve adding another qubit and trying to get them to interact meaningfully. “In the long run, we see a realistic chance of introducing quantum information devices that perform operations faster than a single oscillation of a lightwave,” said Rupert Huber, professor of physics at the University of Regensburg, who led the experiment. “The material is relatively easy to make, it works in room temperature air, and at just a few atoms thick, it is maximally compact.”

Arnab Mukherjee

Arnab Mukherjee

A former tech-support desk jockey, you can find this individual delving deep into all things tech, fiction and food. Calling his sense of humour merely terrible would be a much better joke than what he usually makes.