Has the age of quantum computing arrived?
When we say an emerging technology represents a “paradigm shift,” it’s often a hyperbole. In the case of quantum computers, it’s an understatement …
Ever since Charles Babbage’s conceptual, unrealised Analytical Engine in the 1830s, computer science has been trying very hard to race ahead of its time. Particularly over the last 75 years, there have been many astounding developments – the first electronic programmable computer, the first integrated circuit computer, the first microprocessor. However, if as Moore’s Law states, the number of transistors on a microprocessor continues to double every 18 months, the year 2020 or 2030 will find the circuits on a microprocessors measured on an atomic scale. And the next step may be the most revolutionary of all. Quantum computing is the technology that many scientists, entrepreneurs and big businesses expect to provide a, well, quantum leap into the future.
The concept of quantum computing is relatively new, dating back to ideas put forward in the early 1980s by the late Richard Feynman, the brilliant American theoretical physicist and Nobel laureate. He thought of the possible improvements in speed that might be achieved with a quantum computer. But theoretical physics, while a necessary first step, leaves the real brainwork to practical application.
In order to explain quantum computer first we must to explain the basic concepts that conventional or classical computer are based upon. Classical computers are based on billions of transistors, which represent the simplest form of a data processor. Transistors are essentially switches that can either block, or open the way for incoming information. This information is stored in binary bits, meaning that a single bit can be in one of two states, a “1” or a “0”. You could think of this as a light bulb switch where ON represents 1 and OFF represents 0.
Unlike conventional computers, quantum computers store and process data using quantum bits or “qubits”. Qubits can be atoms, ions, photons or electrons. The advantage of using qubits is that they can be in more than one state at a time. Each qubit can assume a value of a 1 or a 0 or both of these numbers simultaneously.
You might ask how is this possible? Well, in the case of electrons, they all have a magnetic dipole, so they’re basically like tiny bar magnets. This property is called its spin. An electron can be spin up or spin down, like the classical 1 or 0. In a quantum computer, electrons align with the magnetic field that they are in, just like a compass needle aligns with the magnetic field of the Earth. Now since this is their lowest energy state, the electrons are in the spin down state. However, each individual electron can be forced into the spin up state if it is hit with a pulse of electromagnetic waves. So you could think of the electron as like a radio that can only tune in to one station, and when that station is broadcasting, it gets all excited and turns to the spin up state. However, if the station doesn’t broadcast for long enough, the electron becomes stuck between the two states. A proportion of it is in the spin up state (1) and a proportion of it is in the spin down state (0). This is what’s known as quantum superposition, and in a quantum computer it allows the qubit to be in both a 0 and a 1 state at the same time.
As pair of bits can be in one of four different states, 0,0 0,1 1,0 1,1. In comparison, a pair of qubits can be in all four of these states at the same time due to at any one time. This means that a quantum computer with n quits can be in an arbitrary superposition of up to 2^n states simultaneously unlike a normal computer where the bits can only be in one of these 2^n states at any given time. As such, quantum computers are exponentially faster than normal computers.
There are a few problems associated with using quantum computers. The superposition of states represents Shrodingers famous thought experiment – a cat and a vile of poison are trapped in a box. Until you open the box, the cat is both alive and dead at the same time. However, this means that when you do open the box, you see either that the cat is alive or dead. The same concept applies to quantum computing. As long its not observed, the qubit is in a superposition of probabilities for a 1 and a 0 state. But the instant you measure the spin of the qubit to read the information encoded into it, the probability distribution collapses and the qubit assumes one of the defined states. One way around this is to measure qubits in parallel, thus giving multiple values for a single qubit. Another problem for quantum computers is that the algorithms they use are probabilistic, in that they provide the correct solution only with a certain known probability. The last obstacle for quantum computers is that they need to be in a supercooled environment (-273C) to maintain superposition and entanglement. Any intrusion of heat or light corrupts the computing process and thus the effectiveness of the computer.
Entanglement is another really weird and unintuitive property of qubits. It is a close connection that makes each of the qubits react to a change in the other’s state instantly, no matter how far apart they are. This means that by measuring just one entangled qubit, you can directly deduce the properties of its partner’s without looking. Entanglement provides physicists with the ability to indirectly measure qubits without actually having to look at them.
So how do quantum computers actually solve quantum algorithms? Well in nature, physical systems tend toward their lowest energy state: objects slide down hills, hot things cool down, and so on. This behaviour also applies to quantum computers processing quantum algorithms. To imagine this, think of a hiker looking for the best solution by finding the lowest valley in the energy landscape that represents the problem.
Classical algorithms seek the lowest valley by placing the hiker at some point in the landscape and allowing that hiker to move based on local variations. While it is generally most efficient to move downhill and avoid climbing hills that are too high, such classical algorithms are prone to leading the hiker into nearby valleys that may not be the global minimum. Numerous trials are typically required, with many hikers beginning their journeys from different points.
In contrast, quantum annealing begins with the hiker (qubit) simultaneously occupying many coordinates thanks to the quantum superposition. The probability of being at any given coordinate smoothly evolves as annealing progresses, with the probability increasing around the coordinates of deep valleys. Quantum tunneling allows the hiker (qubit) to pass through hills—rather than be forced to climb them—reducing the chance of becoming trapped in valleys that are not the global minimum. Quantum entanglement further improves the outcome by allowing the traveler to discover correlations between the coordinates that lead to deep valleys. Therefore, quantum computers are especially useful in terms of optimisation problems, and present a much faster method of obtaining the correct answer.
In conclusion, quantum computers are devices mainly designed to solve complex problems, which require us to deal with very large amounts of data. The role of a quantum computer is to provide assistance in capturing what is beyond the boundary constrained by time and energy needs. Perhaps, in the not so distant future, we will be able to climb up the ladder to a new rung of possibilities, such as the creation of new drugs, breakthroughs in research on climate change, and the development of new technological devices. It is the hope that these new discoveries will provide us with a deeper understanding of the reality that surrounds us. And all of this is thanks to the laws of nature and the desire to explore which defines humanity.
Richard Phillips Feynman (May 11, 1918 – February 15, 1988) was born to a sales manager and a homestay mother in Queens, New York. He was an American theoretical physicist, most commonly known for his contribution to the field of quantum mechanics. However, did you know that his work in theoretical physics led him to help develop the atomic bomb during World War II? Another one of famous contributions was to quantum electrodynamics, where he along with two other physicists, earned the prestigious Nobel Prize in Physics in 1965. Feynman was also credited with founding the field of quantum computing as well as the concepts behind nanotechnology.
From a young age, Richard, or Ritty as his friends called him, learnt a great deal of science from Encyclopaedia Britannica and taught himself elementary mathematics before he had even learnt it at school. He also set up a laboratory in his room at home where he experimented with electricity. In particular he wired circuits with light bulbs, and he took radios apart to repair damaged circuits. In fact, he loved experimenting so much so that at the right bold age of 9 he created a home burglar alarm system while his parents were out. In the same year, Feynman’s sister, Joan was born. Despite the 9 year age gap the two got along well, and Feynman even encouraged his sister to pursue a career in physics despite their mother’s disapproval. She later went on to specialise in astrophysics.
Feynman died on the 15th of February, 1988 in Los Angeles due to a rare form of cancer known as liposarcoma which caused his kidney to fail. According to D L Chandler, “Feynman was widely known for his insatiable curiosity, gentle wit, brilliant mind and playful temperament”. He is regarded as being one of ten greatest physicists of all time and to this day is still dearly missed.