[Image Source: Yuri Samoilov]
Scientists at MIT have successfully developed a scalable quantum computer that runs off of 5 atoms which successfully used Shors algorithm to correctly factor the number 15.
The factors of 15 are relatively simple: just 5 and 3. However, a slightly larger number like 93 will probably take a pen and paper to figure it out. An even larger number with 232 digits can (and has) taken scientists over two years to factor correctly, with the assistance of hundreds of classical computers operating in parallel.
Factoring large numbers is so incredibly hard, that it makes up the basis of many encryption schemes that are used to protect credit cards, state secrets, and other confidential information. The operation is made easy to check with the password that unlocks the algorithm, however, the password is made into a long string of random characters that make decrypting it to the original password practically impossible which would take a classical computer thousands of years to crack by brute force (essentially guessing until the code works).
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In 1994, the Morss Professor of Applied Mathematics at MIT, Peter Shor, derived the quantum algorithm that can calculate all the prime factors of a large number, exponentially faster than a classical computer. However, the success of the algorithm comes from the number of quantum bits- the more bits, the better the algorithm will work. Although some scientists have implemented Shors algorithm in various quantum systems, none have the ability to be scaled up beyond more than a few quantum bits.
That, however, has changed. A paper published in the journal Science from researchers at MIT and the University of Innsbruck in Austria reported that they have successfully designed and built a quantum computer from 5 atoms held in place by an ionic trap. The computer is controlled by laser pulses which carry out Shor’s algorithm on each individual atom, which was able to correctly factor the number 15. The system was built in such a way that it can be expanded using more lasers and atoms to create a bigger and faster computer, that one day could factor much larger numbers (and crack all encryption methods). The results claim to represent the first implementation of Shor’s algorithm which has the ability to be scaled.
“We show that Shor’s algorithm, the most complex quantum algorithm known to date, is realizable in a way where, yes, all you have to do is go in the lab, apply more technology, and you should be able to make a bigger quantum computer.”
“It might still cost an enormous amount of money to build — you won’t be building a quantum computer and putting it on your desktop anytime soon — but now it’s much more an engineering effort, and not a basic physics question.” ~Isaac Chuang, professor of physics and professor of electrical engineering and computer science at MIT
Classical computing involves a binary system where numbers are represented by either 0s or 1s. Calculations are then carried out according to the instructions of a predetermined algorithm which manipulate the 0s and 1s to create both an input and an output. A quantum computer makes use of a quantum property that relies on atomic-scale units, or “qubits”, that can represent 1 and 0 simultaneously- a property known as superposition. An atom in this state (representing one qubit) can essentially carry out two calculations in parallel, making certain computations incredibly more efficient than a classical computer. Although a classic computer can carry out single operations faster, a quantum computer can arrive at the same answer with exponentially less steps.
The team kept the quantum system stable with an ion trap that held the atoms in place allowing them to remove one atom, therefore giving it a charge. The atoms were then held in place by an electric field
“That way, we know exactly where that atom is in space,”
Chuang explains.
“Then we do that with another atom, a few microns away — [a distance] about 100th the width of a human hair. By having a number of these atoms together, they can still interact with each other, because they’re charged. That interaction lets us perform logic gates, which allow us to realize the primitives of the Shor factoring algorithm. The gates we perform can work on any of these kinds of atoms, no matter how large we make the system.”
Chuang’s colleagues at the University of Innsbruck built the apparatus based on Chuang’s team’s design. The computer was directed to factor the number 15 – the smallest number necessary to demonstrate Shor’s algorithm. The system gave the correct factors without any prior knowledge of the answers to a degree of 99% certainty.
Chuang says:
“In future generations, we foresee it being straightforwardly scalable, once the apparatus can trap more atoms and more laser beams can control the pulses. We see no physical reason why that is not going to be in the cards.”
The completion of the apparatus is an astonishing feat that has great potential in cyber security and unlocking the secrets of the universe. However, a scaled computer could see the potential to crack every single encryption system on the planet. Fortunately for frequent users of the net, there are still many years (and billions of dollars) before a quantum computer could successfully crack any encryption method. Chuang and his colleagues have created an engineering marvel by first implementing a scalable quantum computer capable of successfully factoring small numbers.
As we progress through the 21st century, we are discovering more and greater things about the universe we live in. Perhaps one day we will be able to unlock the rest of the universe’s secrets by designing the universe inside a computer, then again, maybe we already have inside our own minds.
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