What is a quantum computer?

The definition of the quantum computer is quite simple. It is a computer that exploits the laws of physics and quantum mechanics for data processing using the qubit as a fundamental unit. Unlike electronic calculation, at the base of computers as we have always known them, whose fundamental unit is the bit!

In particular, quantum bits have some properties that derive from the laws of quantum physics such as:

- The superposition of states (they can be 0 and 1 at the same time) due to which parallel rather than sequential calculations can be made as happens today with the computational capacity of "traditional" computers.

- The entanglement that is the correlation (the bond) that exists between one qubit and another, a very important aspect because it has a strong acceleration in the calculation process derives due to the influence that one qubit can produce on another even if they have distance.

- Quantum interference: It is, in fact, the effect of the first principle (the superposition of states); quantum interference allows you to "control" the measurement of qubits based on the wave nature of the particles. The interference represents the superposition of two or more waves that depend on whether there is an overlap or not between grows and bellies. For instance, higher and lower parts of the wave - constructive interference can occur. When crests or bellies coincide and form a wave, which is the sum of the overlapping waves, or destructive interference when overlapping are the crest of a wave and belly of another, in this case, the two waves cancel each other out.

To understand how we got to the quantum computer, we have to go back to the miniaturization of circuits and Moore's Law. From the 1960s onwards, there has been a progressive increase in the computing power of computers, an increase that has gone hand in hand with the miniaturization of the electronic circuits from which it derives the famous Moore's Law. According to this law, “the complexity of a microcircuit, measured with the number of transistors in a chip (processor), and the relative calculation speed doubles every 18 months ".

Following this law - which over time has become a real measurement parameter and also guide of objectives for processor manufacturers - we have come to have integrated microchips, i.e., processors that integrate a CPU, a GPU, and a Digital Signal inside them processing, within our smartphones.

However, a threshold that today has reached the limits of quantum mechanics, making it very complex (almost impossible) to continue the path of miniaturization, together with the increase in the density of transistors. Limit that has actually opened the way to a paradigm shift trying to exploit the laws of physics and quantum mechanics to achieve a computing power higher than that of computers based on electronic calculation without necessarily thinking about the miniaturization of circuits.

The information units that encode two states open and closed (whose values are 1 and 0) of a switch, exploit those that are called qubits. The units of quantum information that are coded not by 1 or 0 but by the quantum state in which a particle or atom is found, which can have both the value 1 and the value 0 at the same time. Moreover, in a variety of combinations that produce different quantum states (a particle can be 70% in state 1 and 30% in state 0, or 40% and 60%, or 15 and 85).

A condition that takes on an incredible meaning when you think of mathematical progression such as 2 qubits can have 4 states simultaneously.  For example, a pair of qubits can be in any quantum superposition of 4 states), 3 qubits can be in any 8 state superpositions. And, eight strings of three different bits: 000, 001, 010, 011, 100, 101, 110 and 111), 4 qubits in overlapping 16 states, 8 qubits of 256 states and so on. In a quantum computer, the n qubits can be in any superposition up to 2 to ‘n’ different states.

In fact, atomic and subatomic particles can exist in an overlap of quantum states, a situation that greatly expands the possibilities of encoding information by opening the possibility of exploiting this processing capacity for the resolution of extremely complex problems, such as those underlying the Artificial intelligence.

How a quantum computer works (overlapping states and entanglement)

The critical issues that have so far slowed down the race to develop these systems are related to the controlled manipulation of atoms and particles. It is possible with a few qubits but for complex processing hundreds and thousands of qubits are needed. Their connection and communication, as well as the development of algorithms are suitable for the quantum computer.

The functioning of the quantum computer, as mentioned in the first paragraph of this service) is based on two laws of quantum mechanics:

- The superposition principle from which derives, as we have seen, the possibility for the particles to be simultaneously in several different states. The superposition of states, in quantum physics, represents the simultaneous existence of all possible states of a particle or physical entity before its measurement. Only with the measurement, it is possible to define precisely the property of the qubit, and this is one of the most critical aspects that have not yet made the quantum computer available on a large scale. The particles are unstable, and their measurement is very complex, to which it must be added that the instability of the particles generates heat, which, to date, can only be controlled with advanced cooling systems.  

- The quantum correlation (entanglement): It expresses the constraint, the correlation precisely that exists between two particles or two qubits.

According to this principle, it is possible to know the state of a particle (or a qubit) by measuring the other with which it has the constraint. 

Quantum Computing: potential applications of the quantum computer

According to Gartner analysts, applications for quantum computing will be restricted and targeted, as the general-purpose quantum computer - most likely - will fail to be economically accessible on a large scale (at least not in the short term).

However, technology has the potential to revolutionize certain sectors. Quantum calculation could allow discoveries and be applied in many sectors:

- Machine-learning:  improved machine learning due to a faster forecasting structure (due to parallel calculation). Examples include quantum Boltzmann machines, semi-supervised learning, unsupervised learning, and deep learning.

- Artificial intelligence:  faster calculations could improve the perception, understanding, and diagnosis of circuit faults / binary classifiers.

- Chemistry:  New fertilizers, catalysts, battery chemicals will bring enormous improvements in the use of resources;

- Biochemistry:  New drugs, customized drugs, personalized medicine.

- Finance: the quantum calculation could allow the so-called faster and more complex "Monte Carlo simulations"; for example in the field of trading, optimization of "trajectories," market instability, price optimization, and hedging strategies.

- Medicine and health:  DNA gene sequencing, such as optimization of radiation therapy treatment/brain tumor detection, could be done in seconds rather than hours or weeks.

- Materials: super-resistant materials; anti-corrosive paints, lubricants, semiconductors, the research could be greatly accelerated due to super-fast calculations.

- Computer science:  faster multidimensional search functions, for example, query optimization, mathematical calculations, and simulations.

Author: Vicki Lezama