Quantum Communication

— A frequent and common aspect in the world of cybercrime is the hacking of sensitive information. Transmission of personal and financial information without the knowledge or permission of an individual or organization can have unconceivable pernicious effects. Money can be stolen, and personal information can be used for unlawful purposes. The enormous threat caused by cybercrime or cyber-attacks is pressing various government organizations, businesses, and other vulnerable departments to discover more reliable means of communicating and transmitting the information. The laws of quantum physics are used for protecting data in quantum communication. The quantum mechanical counterpart of a classical bit is a quantum bit or a qubit that can exist in a state of superposition. A qubit can be in a state of 0 or 1 or a linear combination of both.


INTRODUCTION
Data protection along with the secure transmission of data is very challenging and is of vital importance today. Quantum communication envisages communication and transmission of data in a secure manner using various advanced technologies. Laws of quantum physics allow particles to exist in multiple combinations of 1 and 0 concurrently. Hence, qubits can exist in any superposition of 1 and 0 and therefore store a lot more information than just 1 or 0.
For protecting data against eavesdropping, quantum cryptography is being used during the transmission of data. The most extensively developed and used application of quantum cryptography is Quantum Key Distribution (QKD). Another vital element in quantum communication is a quantum network that allows us to transmit information in the form of qubits between physically separated quantum processors. A quantum computer that can perform quantum logic gates on qubits is referred to as a quantum processor. Local quantum networks can be connected to a quantum internet that supports many applications. Companies or businesses that need to protect their important and valuable data will find the quantum internet particularly fascinating.
Currently, physical quantum computers are extremely noisy. Though many organizations and governments are investing considerable amounts in quantum computing and a lot of research is also going on in the field of quantum error correction, it may take time to be fully developed.

II. QUANTUM KEY DISTRIBUTION
Quantum communications depend on the quantum properties of photons and it is more secure than other methods implemented through coding. However, building quantum communication systems is significantly more expensive.
At present, data encryption techniques are used for the secure transmission of sensitive data. When data is encrypted it passes through a cipher that uses an algorithm to encrypt data using it to a key. The data and the keys are then sent as electrical or optical pulses representing 1s and 0s. A powerful cryptosystem has countless possible keys, so an attacker would be unlikely to seek out the right key by using a brute force approach.
Photons are used to exchange key data between users in Quantum Key Distribution (QKD). Each photon denotes a single bit of data whose value is determined by states of the photon such as polarization or spin. The sender generates a sequence of photons and each photon is either horizontally or vertically polarized. This polarization is measured by the receiver. If an attacker intercepts the photon to determine its polarization, the photon is destroyed in the process. The attacker would have to produce an identical photon to send to the receiver to avoid getting detected. However, the photon also has a second property, spin. According to the uncertainty principle of quantum physics, it is impossible to determine both properties of the photon accurately at the same time. This makes it impossible for the attacker to send an accurate duplicate. The receiver would find a high error rate in the photons being received which would signify that data had been intercepted.
For calculating the error rate, the states of some photons are compared over a different channel. This comparison destroys the photons and they cannot be used to create a key. The error rate is used to check whether the session is secure. If it is indeed secure, some number of photons can be selected as the bits of the key.
As of now, there are some crucial challenges with QKD. The cost of QKD systems is high and it is not robust. Hardware and software for chip-based QKD are still in an inchoate phase. Also, original data is being transmitted via conventional networks. Hackers can copy the bits unnoticed and then try to crack the key used for encryption of the data using powerful computers.

IV. CONCLUSION
Data protection is a necessity today as the volume of data created and stored grows at an unparalleled rate. Quantum communication and quantum computing are growing fields and many leading computing groups, universities, and organizations are exploring this topic. This pace is likely to increase further even though practical machines are still a few years away The target is to eventually move away from experiments in which we only observe quantum phenomena to experiments where we control them. It is impossible to envisage when we will build the first quantum computer; it could be this very year, in the next decade, or even centuries from now. Some significant technological and conceptual issues remain to be resolved. We need to figure out how to create qubits, how to protect machines from outside world interference, check the machine is functioning, and how to understand the outputs.
In the future, there is a possibility to build complete quantum computing systems that may be used for factoring large numbers and interpreting and encoding messages. Our current methods of encryption may not be resistant to the decryption capabilities of quantum computing. Some tasks like database querying and searching could be accomplished in a fraction of the time taken by conventional computers. Quantum computers could also be used to expand our understanding of quantum mechanics. A full-scale replacement of conventional computers is improbable even though quantum computers are likely to play a very significant role in the future.

V. ACKNOWLEDGEMENT
I would like to express my sincere gratitude to my mentor, Mr. Chhatrasal Chandra for his guidance. I would also like to thank my family for their support.
Author contribution: I am the sole author.