Quantum Information Sciences and Communications Laboratory

Quantum Information Science

The fundamental nature of quantum information science attracts me the most. It is changing the definition of what is considered computable. One of the most famous examples of distributed computation is quantum teleportation where two parties share entangled qubits and can use these to reconstruct an unknown qubit using simple (quantum) gate operations. While this has led to comparisons with Star Trek, quantum teleportation will be the key technology in enabling long distance quantum communication and quantum Internet. It can be used for secure transmission of arbitrary quantum states. However, the cost of teleportation remains high requiring two classical bits in addition to a pre-shared entangled qubit. With gigabytes of data being transferred, such cost does not scale.

The cost for teleportation has remained stuck for almost three decades. There have been minor advances in it where one could use fewer classical bits if the qubits to be transmitted are chosen from a restricted state space but that is not very useful for general purpose computation. In a result (https://www.nature.com/articles/s41598-022-06853-w) I proposed a new method for reducing the cost of teleportation to 1.25 bits from 2 bits. By demonstrating a tighter bound on the cost of teleportation it provides a new means to assess protocols like superdense coding, Holevo bound and many quantum cryptographic protocols that depend on quantum entanglement and teleportation. It also breaks the long-assumed symmetry in quantum systems where on one hand two bits were required to teleport, and the other hand two bits could be encoded onto a qubit. This result also provides one party in a quantum cryptographic protocol a means to cheat and gather more power than the other party, which is devastating for these protocols.

My research directions in quantum information science are as follows,

1. Develop new quantum key agreement protocols considering my above-mentioned result to prevent bias and cheating.

2. Develop multi-photon quantum cryptography for higher key generation rates and transmission distances.

3. Integrate multi-photon quantum cryptography and teleportation with quantum router-based networking protocols for congestion control.

4. Developing new protocols for threshold quantum cryptography for IoT devices and edge computing.

Secure Quantum Communication Networks

The primary function of the Internet is to allow for one party to send messages to another in a reliable and secure manner. Over the years the technology has evolved considerably and with the advent of public-key technology and the public-key infrastructure it has become pervasive. However, the guarantees of confidentiality and authenticity of messages that classical cryptography provides has been fledging overtime. The reliance of public-key infrastructure on unproven mathematical assumptions is not a viable strategy in the long run. Quantum Internet essentially fills this void by basing the security of the communication on fundamental laws of Physics such as superposition, no-cloning theorem and the use of quantum gates and algorithms. Guarantees of confidentiality and authenticity provided by such an infrastructure will not disappear with advances in computing power and mathematical techniques overtime.

Rapid advances in quantum material science in recent years has made it possible to develop and deploy many of the prototype quantum algorithms over large scale geographic distances. Companies such as Toshiba, IDQuantique, IBM, Google and Intel have ongoing quantum computing projects both in hardware and software. The new Quantum Internet is envisioned to enable secure communications and blind computing using a distributed infrastructure where several distant quantum computers are interconnected using quantum entanglement.

My current research in this area is focused on an efficient integration of quantum security principles into a quantum communication networks that coexist and interplay with classical networks. Quantum networks present challenges of their own because of the unstable nature of quantum bits that often decohere (decay) at an exponential rate. Limited capability of today’s quantum repeaters limit transmission distances as well as increase in attack surface due to incorporation of trusted nodes. However, the efficiency and distance of secure quantum communications is highly dependent on network topology and the quantum cryptography protocol used on that topology. Further, new techniques such as entanglement swapping are making older cumbersome single photon quantum cryptography protocols obsolete/unnecessary and therefore development of new protocols that take full advantage of entanglement swapping is imperant. Furthermore, limitations of manufacturing technology are forcing the use of non-ideal quantum signal emitters and require network scientists to rethink some of the hardware assumptions in play on quantum internet. My research is therefore motivated by the following goals,

1. Develop novel quantum protocols that take full advantage of fundamental network topologies to reduce error rates.

2. Remove hardware dependency of quantum security protocols.

3. Develop noise-intermediate scale quantum security protocols that can take full advantage of non-ideal hardware components to extend transmission distances.

4. Investigate secure configurations of quantum satellite-based constellation networks for long range quantum networks.