A horde of quantum processers
Before getting into the concept of quantum computers, let’s briefly compare the types of quantum computers. Gate quantum computer being the most familiar one performs the calculation by using discrete logic operations by using a collection of gates, while the answer is read out at the end.
However, Adiabatic quantum computing does not involve isolated operations. As an alternative, the problem is altered to be the lowest-energy state of some energy landscape. The technique is, to begin with, a landscape that appears like a smooth bowl and slowly create the mountains so that the qubits fall into the lowest valley when the process is complete. The solution to the problem lies in reading out the values of the qubits.
The third one is optical quantum walks; however, it is totally different from the above two. The optical quantum walks have each device fixed: the coupling between fibers and the length of fibers cannot be promptly adjusted. Basically, a computer working on the fundamental of optical walks requires a programmable element.
The matter that flows like light
In a Bose-Einstein Condensate, the role of matter and light is interchangeable. The BEC is a conjunct of very cold atoms that are all in the same quantum state, meaning that the collection works like a single particle. When the BEC is hit with a pulse of light, it receives momentum and kicks, causing it to drift. Nonetheless, the direction of the drift is completely dependent on the internal state of the BEC.
A microwave pulse sets the internal state of BEC. So, for example, the correct microwave pulse will congeal the BEC into a superposition of two states. If a laser kick follows the microwave pulse, then the BEC is forced to move in two directions at once due to that superposition.
The researchers have further demonstrated that the three-dimensional path of the BEC can be modified by sequences of laser pulses and microwaves, while the controller acts like a skilled pinball player. However, this is a quantum pinball: every time the BEC hits a bumper, the ball hits multiple additional bumpers and the ball goes in multiple directions.
Worsening it further, the balls cross paths and recombine at various points. The BEC interferes with itself, where the paths overlap. While increasing it on others, the interference reduces the probability of finding the BEC on certain paths. This is exactly what we desire for quantum computations.
The BEC version is found to be more flexible where light demands glass fibers with fixed coupling between each other. As the microwave pulse acts like couplers between different paths, the light kicks move the BEC along in free space.
The key point is that the strength of the microwave pulse changes the coupling between different paths, while the number of light pulses changes the path length.
As none of the two aspects – the light, and the microwave pulse – are fixed, they can be altered at any given time making the route more programmable.
The computer here is absent. The researchers have proved the fact that a single BEC can be made to go through a quantum walk. However, they have not demonstrated that a problem can be encoded in that walk.
On the other hand, this is a good start. Potentially BEC quantum walks are able to combine the best of several worlds. They rely on neutral atoms and operate in the clean. We are expecting a highly reliable and long-lived quantum bit, offering prospects for scaling.