Researchers Prasanta Panigrahi (left) and Sreraman Muralidharan. 
Hackers have been the most formidable enemies of net-savvy people. With a stolen password, malicious software, personal computer and internet connection, they sneak into secret domains like personal email and wreak havoc with masked identities. Unlike classical computers, which encode message in binary digits or classical bits (0s or 1s), quantum computation encodes messages in quantum bits or 'qubits'. A qubit can be 0 as well as 1 or a superposition of both. Using the new methods, the researchers split the quantum information (qubits) in ways that sharing of quantum information between various parties remains secure against hackers.
"This quantum information splitting (QIS) will have far reaching implications in defense, banking and other sectors which need secure multi-party information sharing," says lead researcher Prasanta Panigrahi of the Indian Institute of Science Education and Research (IISER) Kolkata and Physical Research Laboratory, Ahmedabad.
Sharing information between multiple parties in a secure environment is of great interest. For the study1, the researchers created three hypothetical parties – Alice, Bob and Charlie to share quantum information. Then they employed single-qubit and two-qubit states. A single qubit system refers to the state of a single particle. A two qubit system refers to a composite system of two particles. Such particles can be photons or spins in quantum dots or ions in ion traps. In single-qubit state, Alice possesses qubit 1, Bob possesses qubits 2 and 3, and Charlie possesses 4. In two-qubit state, Alice has qubit 1, Bob qubit 4, and Charlie possesses 2 and 3.
The trio carries out measurements on their qubits that harbour quantum information. One needs classical bits to convey the outcome of the measurement performed on qubits and not to send qubits. The outcomes of the measurement performed by Alice and Bob dictate the state obtained by Charlie. For Charlie to know the outcome of the measurement on Alice's and Bob's qubits, it is encoded into cbits (classical bits) and transmitted to Charlie.
To test whether the information sharing between them is secure, the researchers exposed the qubit systems to a hypothetical hacker 'Eve'. To eavesdrop, the hacker used 'Ancilla' a qubit, which is a stranger to the quantum channel used for information sharing by Alice, Bob and Charlie. But 'Eve' failed to decipher what they shared.
The researchers say that they have considered a type of hackers' attack commonly employed in the quantum domain. "A stronger crypto-analysis of our schemes against Trojan horse, a malware that allows unauthorized access, and other type of attacks is under investigation," adds Panigrahi.
Quantum information sharing of a single qubit state has been realized using photons and ion trap systems. "However, sharing of a two qubit system has not been experimentally carried out in literature. It can be implemented, in principle, using both photons and ions," says co-researcher Sreraman Muralidharan of Loyola College, Chennai. "Right now, we are investigating a crypto-analysis of our schemes and developing quantum circuits for them," he says.
