According to Gruska (2004), this is a crucial concept in the context of quantum information theory and quantum computing, but also, it can be considered as the most puzzling in the quantum physics paradigm. Through entanglement, quantum particles exist in strong and perfect correlation so that they are linked together, even when separated by great distances. According to the Institute for Quantum Computing (2013), these particles are intrinsically connected so that, even when positioned at opposite ends of the universe, they can dance in perfect unison, thereby inspiring Einstein to name the interrelation as spooky action at a distance (Institute for Quantum Computing, 2013).
Photons and Polarization
A photon is referred to as a quantum of electromagnetic energy. According to Rieffel and Polak (2011), quoting Einstein, light is composed of packets of energy referred to as photons. Light quanta have no mass, but possess momentum hence energy given by the formula E= hf. In this case, h is the Plancks constant and f is the frequency of the radiation. Polarization is a photon property, and is basically the plane upon which its electric field oscillates. Different polarization can be used to represent a variety of quantum states, which is made possible by use of a polarizer or a Pockels Cell. Possible states are encapsulated in the rectilinear (0 and 90) and the diagonal (45and 135) polarizations. In this case, quantum computing recognizes these polarizations in binary, where 0 and 45 configurations are assigned a 0 while the 90, and 135states are assigned a 1.
The quantum no-cloning theorem, as encompassed in quantum mechanics, prevents the creation of unknown copies in the quantum states (Cobourne, 2011). As such, according to Lo and Zhao (2012), this theorem holds that it is impossible for an eavesdropper to make any additional copies of unknown quantum state, which offers a protection mechanism in quantum computing. In line with this assertion, it is impossible to amplify quantum signals. Therefore, as per the theorem, quantum cryptography guarantees forward security as the eavesdropper cannot transcript quantum signals from Alice to Bob.
Limitations of Quantum Computing
One of the major limitations for quantum computing is decoherence, which can be referred to as the sensitivity to environmental interactions, usually coined quantumness. According to Ponnath (2006), it is difficult to isolate the system without environmental entanglement, which is aggravated by larger number of qubits. In addition, Cobourne (2011) point out that minimizing decoherence is a major technical challenge in quantum computers.
Availability of Quantum Computers:
Despite the fact quantum computers are already in existence, they do not have a sufficient power to replace classical ones. They are yet to be developed to full capacity. For instance, according to the Institute for Quantum Computing (2013), the D-wave quantum computers that is currently being used by world class organizations, such as NASA, Google, Lockheed Martin, as well as the University of Southern California has some problems with its performance. However, in an effort to better it, experiments are being done to eliminate the problems it currently faces. In order to better these quantum computers, IQC and MIT researchers are investigating means of fabricating better quantum computers, and currently, they hold a record for being the researchers who have used the most qubits in an experiment Institute for Quantum Computing (2013). As such, it is imperative to note that a quantum computer that can outperform a classical one is still on its way.
As a result of continuous research efforts, practical quantum technologires are emerging, including the QKD approach, as well as fabrication of highly effective actuators and sensors among other devices, therefore, it can be derived that a quantum computer that has the capability of outperforming the conventional classical computers is still years away (Institute for Quantum Computing, 2013). This owes to the fact that theorists are continually researching to find better ways to overcome the aforesaid limitation of decoherence, as well as experimentalists who are continuously coming up with breakthroughs in quantum instruments and technologies. These pioneering efforts are bound to pave way to the quantum computer era (Institute for Quantum Computing, 2013).
As a matter of fact, QKD technology is already commercially available, including BB84 protocols that entail quantum entanglement which have successfully been used to distribute keys via air and optical fibers, thus ensuring security when broadcasting high security profile messages between Alice and Bob Cobourne (2011). For example, the technology was handy during the 2007 Swiss elections, whuile the Chinese are currently capitalizing on it for trade secret protection. The only limitation is that they can only be used within a radius of 148 kilometers. Currently, there is a couple of companies offering commercial QKD, including ID Quintique, MAgiQ Technologies, SeQureNet, and QuintessenceLabs (Dillow, 2013).
In addition, the Institute of Quantum Computing (2013) is currently experimenting on quantum encryption through free space via the use of satellites. Even though the fabrication of a fully functional quantum computer is the main goal, many discoveries have been made in the process, such as the development of the aforementioned actuators and quantum sensors. These have allowed scientists to navigate the world on a Nano-scale with increased sensitivity and precision. In essence, these tools will be crucial iun the development of quantum information processors, thereby evidencing the ongoing quantum revolution.
Approaches for Building Quantum Computers
According to the Institute for Quantum Computing (2013), quantum machine constriction requires that the qubits should behave in a controlalble manner, and as expected, they are made up of electrons, atoms, or molecules. To control the way they behave, microwave signals are required, which significantly manipulate them. Many reserachers are investigating how larg qubit arrays can be used in designing the operability of quantum computers. However, due to the aforementioned concept of decoherence, they are tricky and difficult to manupulate as they decohere, refferring to the way in which they fall out of their quantum state (Institute for Quantum Computing, 2013). As such, it is essential to combat decoherence so as to improve quantum error correction.
Due to this, most prototype quantum computers are based upon cesium and diamonds, which are expensive, so as to diminish external interference, but operate at freezing temperatures (Borghno, 2015). As such, this has elicited research on the use of cheaper materials, such as silicon. However, as Borghno points out, quantum processors can also be fabricated using other technologies, including Bose-Einstein condensates, nuclear magnetic resonance, and iron trap quantum processor.
Future of Quantum Computing
Because decoherence is one of the factors that lead to quantum information errors, companies, such as Google and IBM, counter this by capitalizing on a new technique referred to as quantum error correction (Hsu, 2015). IBM can now detect errors, but cannot correct them. Therefore, both IBM and Google are reseraching on error correction techniques, which will pave way to future quantum computing systems that will exceed current computer complexities and reliability (Hsu, 2015).
Additionally, decoherence affects QKD performance because of the distance limitation. As Jacob (2015) points out, the longer the distance with which the photons have to travel, the more they will be lossed. As opposed to the 148-kilometer limit, ID Quantique is currently working on a 650-kilometer QKD optical fiber, as well as a 2,000-kilometer fiber by the Chinese government that will link Shanghai with Beijing by 2016 (Jacob, 2015).
Furthermore, existing applications that quantum cryptography will better perform in the future include Quantum Internet. Sasirekha and Hemalatha (2014) argue that conventional internet is fast but its security is paltry, which can benefit by leveraging on quantum-encrypted transmissions, guaranteeing excellent security. Even though it slows down the internet, futuristic developments will enable people to switch easily from a regular to a quantum encrypted internet, thus facilitating the secure transmission of sensitive information.
After reading previous sections, there are obvious questions that came in mind. For example, what would happen if quantum computers emerge in upcoming years? Is it true that all our transactions and important secret operations would be in danger or available to eavesdroppers who will use quantum computers? Then what is a practical solution for that? The answers could not be simple. Indeed, as mentioned previously that almost most of public key cryptography can be easily broken by quantum computing attacks based on Shors algorithm. Additionally, any security protocols that derive security from this public cryptography could be susceptible to quantum computing attacks.
That means all data encrypted using current standard based security systems such as SSL, or TLS, used for e-commerce and Internet banking protection, and SSH used for protection of sensitive computing systems which would otherwise be at risk. Because these protocols are not methods of securing data, but they are a way of negotiating the right security tools, hence meaning that the security depends heavily on encryption algorithms that are used in these protocols. This opens up other questions such as, when will quantum computer accomplish these threats? And how may qubits are needed to break public key cryptography such as 2048-RSA which is considered secure today? In fact, the development of quantum computers is still at the beginning and the kind of quantum computer that have been built until now are considered small and do not break the secure public key cryptography like 2048-RSA. Even though there is a quantum computer called D-WAVE that has 1000 qubits as mentioned previously, there are lots of limitations and very high error rates on its qubits.
Researchers and scientists are still working to enhance this quantum computer by looking for a technique to improve error detections and corrections. Consequently, it seems that researchers and scientists first need to solve all the limitations of the quantum computer, and second to build quantum computers with at least 4000 qubits to break 2048-RSA keys. (Moses, 2009). After solving these two important obstacles then the quantum computer would be a real threat. However, we must be ready to face this threat by focusing on developing the cryptographic technique that do provide protection against quantum computing attacks; known as quantum-safe.
There are some cryptographic techniques that are somewhat vulnerable to quantum attack, but can be easily upgraded to become a quantum-safe, this includes AES. Nowadays, AES-128 is considered very secure because it is difficult for classical computers to break it, and that would take more than billion years to crack it. However, AES-128 can be broken faster by implementing Grovers algorithm in a quantum computer. This algorithm requires 2^(n/2) steps to break symmetric algorithms rather than 2^n that classical computers need to brute-force symmetric algorithms. This means to break AES-128 by Grovers algorithm that would require just 2^64 steps. However, by doubling key size it will become hard for the quantum computer to break AES-256 as similar as for classical computer to break AES-128 because that would require 2^128 steps, and it would be irrational tim...
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