ISRO’s Space Application Centre and Physical Research Lab, Ahmedabad have developed real-time quantum key distribution (QKD) communication between two premises separated by 300 meters. A channel has been created to share text, image and video. It has been repeated to test its robustness.
It is secured encrypted communication. If two particles have to exchange encrypted information, they must share the same key or keys to encrypt or decrypt data. The key is transferred and the encrypted data is transferred. The communication is secure through quantum protected cipher keys. If there is interception of either key or data from either party, they may be able to decrypt the information.
Entangled atoms change the state when someone interferes with the transmission of data. Entangled atoms could be in clockwise or anticlockwise spins. Suppose one atom is sent with encryption key, If someone snoops on the transmission, it causes a change in the spin of the atom. It affects the overall quantum state of the system. The snooping thus gets detected.
The experiment uses quantum physics. The Uncertainty Principle states that it is impossible to know the exact velocity and exact position of a particle at the same time. The velocity or position can be calculated to a precision, but not both at the same time.
The Observer Effect states that the act of observing a particle changes its state and disturbs it. It leads to superposition concept. A quantum bit or Qbit is both on and off due to superposition; and therefore can store much more information than a normal bit. It does number crunching faster. It could make them capable of breaking current encryption.
Elementary particles are not only particles, but they are waves. A wave has a probability of being in one place or another, or doing one thing or another. This happens till it is observed. Once under observation, it collapses and becomes a particle, during something specific.
Entanglement is another key quantum effect. Particles can be paired. If the state of one paired particle changes, the state of the other paired particle instantly changes. This is true for any distance.
The paired particles know instantly about the changes in each other’s state even when separated by distances.
Quantum cryptography uses these concepts. Entanglement enables the setting up of secure keys. A quantum-entangled transmission has a built-in alarm. If two entangled particles are separated, a change in the state of one causes a change in the state of another. If the transmission is intercepted, the observer effect, leads to changes in the state of paired particle. The users thus know immediately whether the communication system is being snooped.
No-cloning concept means that it is impossible to copy a quantum communication for being cracked later.
QKD can be scaled up for greater distances. China has perfected it over 40 km. It is endeavouring to develop such a system for satellites. ISRO too intends to scale up.
It is difficult to handle Qbit which either on or off, and when observed the waves collapse. Quantum system must be kept very cold, and stored in stable places. Quantum computers need to be kept very cold, just a tad above absolute zero.
On 5G fibre network, one can install QKD at key hub locations to protect the traffic. QKD is a method of communication that allows two parties to create a shared random key that is known only to them,