INTRODUCTION
According to Moore’s law, number of transistors in processors double almost every 2 years, however due to physical restrictions it is believed that this number will stop growing in a few decades. Scientists already have to deal with problems which classical computers are unable to solve, for example, simulations of atomic quantum systems. For this very reason researchers all around the world started to put their efforts into creating a fully functional quantum computer.
HOW DO QUANTUM COMPUTERS WORK?
As you might know, classical computers operate in bits, which can have one of the two values at the time: either 1 or 0. However, quantum computers operate in quantum bits or qubits, which are usually represented by such particles like atoms, ions, electrons, and photons. All of these particles have a property called superposition, which means that they can be of two states at the same time, that is a qubit can represent both 1 and 0 at the same time. To put it simply we can illustrate superposition with a famous physicist’s Erwin Schrodinger’s thought experiment: if we put a living cat in a closed box rigged with a device that can randomly release poison (there is equal probability that it will release and won’t) we can say that until we open the box to check the state of the cat, it’s both dead and alive at the same time. And that’s the whole reason why quantum computers are superior to classical ones. For example, a 3 bit register can save only one of the 8 (23) possible bit combinations at the time, but a quantum register of the same size could save all of the combinations at the same time. To take another example, only 500 qubit quantum register could save a number of possible combinations equal to the amount of all of the atoms in our universe. However, one of the drawbacks of the superposition is a property called decoherence, that is if we tried to measure the state of the qubit, or because of disturbance caused by other particles, superposition of the qubit would collapse, the qubit would gain only one of the two states, and become just a classical bit. Lets use Schrodinger’s example again: if we opened the box we would see the cat only in one of the two states – either dead or alive. Another property utilized in quantum calculations is called entanglement. It means that if we affected 2 particles in a certain way, they would become linked, and if we did something to one of the particles no matter the distance between them the other one would also become affected accordingly. Also, if one of the particles stopped being in superposition the same would happen to the other one. So that’s how qubits work, now lets talk about how quantum computers operate. First of all, we would have to set qubits in an initial controlled state that represent the problem we want to solve. Then we would manipulate those qubits with a certain sequence of quantum logic gates called quantum algorithm and finally we would measure the qubits to collapse the superposition and get one of the possible qubit combinations where each qubit is represent either by 0 or 1. Because of this probabilistic feature, most quantum computers would provide the correct solution only with a certain known probability however, it is possible to raise that probability by running the algorithm repeatedly.
POTENTIAL OF QUANTUM COMPUTING
So what kind of problems would utilize the full potential of quantum computing? For example, quantum computers are better suited than classical ones for solving problems that have these properties: * The only way to solve them is to guess answers repeatedly and check them; * Every possible answer takes the same amount of time to check; * There are no clues about which answers might be correct.
One of the areas dealing with these kind of problems is cryptography, that is the area of data encryption and decryption. Many data encryption systems, like RSA utilized for safe data transfer, are based on the notion that it is really hard to factorize very large numbers, composed of hundreds of digits, using classical computers, while quantum computers could do this quite efficiently, for example, with Shor’s algorithm. Also these computers could break security systems with brute force method considerably faster, by utilizing Groover’s algorithm. However accordingly quantum computers could encode data more safely. Another area where quantum computers would perform superior than classical ones is the simulation of quantum systems. Chemistry and nanotechnology heavily rely on understanding of these systems, however classical computers can’t simulate them in an efficient manner. But quantum computers could simulate quantum physics processes exponentially faster and would be extremely useful for creating new drugs and materials and for researching particle interaction in particle accelerators. Also quantum computers would perform better in solving optimization problems, when you need to find the best solution out of a range of possible solutions. However it is hard to predict how we will use these computers in the future. I mean for example even the creators of the first digital computers couldn’t predict that in the future we would use them for playing games or browsing social networks.
CURRENT ACHIEVEMENTS IN QUANTUM COMPUTING
Now lets talk about current advancements in quantum computing. The idea to build a quantum computer first appeared 1980s however the research of these machines is still in it’s infancy. Various quantum research centers all around the world are trying out different methods to realize qubits and have built several prototypes however there is no unified quantum computer model like for example all of the classical computer technology is entirely based on transistor systems. Several most popular quantum computer architectures are as follow: * Based on stray nitrogen atoms in a diamond crystal structure. One of the bigger advantages of this architecture is that qubits can retain their stability and superposition in near room temperature when usually in other architectures cubits must be cooled down to near absolute zero, that is temperature cooler than deep space. * Based on ions trapped in electrical field. Scientists have managed to create a record 14 qubit system using this method. * Based on electron donors in silicon. Using this architecture was achieved record time of how long qubits stayed entangled – whole 35 seconds, which is almost an eternity in quantum world. One of the advantages of this architecture is that silicon based qubit systems can be built using technology already widely used in semiconductor electronics industry. * Based on nuclear magnetic resonance. In this architecture qubits are realized by atoms in a molecular structure which are manipulated using magnetic resonance. Using this method IBM have created 7 qubit systems and are one of the first who demonstrated actual calculations using qubits: they have managed to successfully factor 21. * Based on superconductors. In this architecture qubits are usually represented by superconducting loops in which current flows in both directions when temperature reaches near absolute zero.
However all of these technologies have to deal with problems like decoherence, difficult entanglement and control difficulties therefor currently scientists can’t build fully functioning quantum computers. According to IBM, a practical universal quantum computer should have: * a big enough number of qubits * qubits that can be initialized to starting values; * quantum logic gates that are faster than decoherence time; * universal quantum logic gate set which could be used for various calculations; * qubits that can be read easily.
It’s interesting to note that despite all of the difficulties that scientists deal with trying to create even the simplest quantum computer, a Canadian private company called D-Wave Systems, claims to have created the world’s first practical quantum computer and even sells them. According to D-Wave their most powerful computer consists of an astounding 1000 qubits made out of superconducting loops and is best suited for solving optimization problems. A lot of scientists argue if D-Wave computer is an actual quantum machine, because during numerous tests it rarely performed better than a regular computer, however after an independent research ran by google it was deduced that D-Wave computer does display certain quantum properties. Despite diverging opinions in the public, several institutions like advanced technology company Lockheed Martin, and Google in partnership with NASA bought their units of D-Wave computers. Apparently, Google has already used their d-wave computer to improve efficiency of image recognition algorithms for phones.
CONCLUSION
To conclude I’d like to say that because quantum computing is still in it’s infancy and scientists struggle to build stable qubits and their systems we probably won’t see fully functional universal quantum computers in the very near future, however it is believed that after a few decades these computers will play a crucial role in data security and creation of new materials and drugs. Even though probably we will never have a personal quantum computer in our pockets we will be able to use their services through internet however like mentioned before it is hard to say in what kind of ways exactly we will use them in the future.