Sumit Nandi - Academia.edu (original) (raw)

Papers by Sumit Nandi

Research paper thumbnail of Wigner's approach enabled detection of genuine multipartite nonlocality and its finer characterisation using all different bipartitions

Cornell University - arXiv, Feb 23, 2022

Research paper thumbnail of Resource state structure for cooperative quantum key distribution

Quantum entanglement plays a pivotal role in a number of communication protocols, like secret sha... more Quantum entanglement plays a pivotal role in a number of communication protocols, like secret sharing and quantum cryptography. We consider a scenario where more than two parties are involved in a protocol and they share a multipartite entangled state. In particular, we introduce the protocol of cooperative quantum key distribution (CoQKD). In this protocol, two parties, Alice and Bob establish a key with the cooperation of other parties. Other parties control whether Alice and Bob can establish the key, its security and the key rate. We discuss the case of three parties in detail and find the necessary suitable resource states. We discuss the controlling power of the third party, Charlie. We also examine the usefulness of this new resource state for generating conference key and for cooperative teleportation. In the case of conference key, we find that recently introduced Bell inequalities can be useful to establish the security. We also generalize the scenario to more than three p...

Research paper thumbnail of Resource state structure for controlled quantum key distribution

The European Physical Journal D, 2020

Quantum entanglement plays a pivotal role in many communication protocols, like secret sharing an... more Quantum entanglement plays a pivotal role in many communication protocols, like secret sharing and quantum cryptography. We consider a scenario where more than two parties are involved in a protocol and share a multipartite entangled state. In particular, we considered the protocol of Controlled Quantum Key Distribution (CoQKD), introduced in the Ref. Chin. Phys. Lett. 20, 183-185 (2003), where, two parties, Alice and Bob establish a key with the cooperation of other parties. Other parties control/supervise whether Alice and Bob can establish the key, its security and key rate. We discuss the case of three parties in detail and find suitable resource states. We discuss the controlling power of the third party, Charlie. We also examine the usefulness of the new resource states for generating conference key and for cooperative teleportation. We find that recently introduced Bell inequalities can be useful to establish the security of the conference key. We also generalize the scenario to more than three parties.

Research paper thumbnail of Two-qubit mixed states and teleportation fidelity: purity, concurrence, and beyond

The European Physical Journal D, 2018

To explore the properties of a two-qubit mixed state, we consider quantum teleportation. The fide... more To explore the properties of a two-qubit mixed state, we consider quantum teleportation. The fidelity of a teleported state depends on the resource state purity and entanglement, as characterized by concurrence. Concurrence and purity are functions of state parameters. However, it turns out that a state with larger purity and concurrence, may have comparatively smaller fidelity. By computing teleportation fidelity, concurrence and purity for two-qubit X-states, we show it explicitly. We further show that fidelity changes monotonically with respect to functions of parameters-other than concurrence and purity. A state with smaller concurrence and purity, but larger value of one of these functions has larger fidelity. These functions, thus characterize nonlocal classical and/or quantum properties of the state that are not captured by purity and concurrence alone. In particular, concurrence is not enough to characterize the entanglement properties of a two-qubit mixed state.

Research paper thumbnail of More communication with less entanglement

The European Physical Journal D, 2015

We exhibit the intriguing phenomena of "Less is More" using a set of multipartite entangled state... more We exhibit the intriguing phenomena of "Less is More" using a set of multipartite entangled states. We consider the quantum communication protocols for the exact teleportation, superdense coding, and quantum key distribution. We find that sometimes less entanglement is more useful. To understand this phenomena we obtain a condition that a resource state must satisfy to communicate a n-qubit pure state which has m terms. We find that an appropriate partition of the resource state should have a von-Neumann entropy of log 2 m. Furthermore, it is shown that some states may be suitable for exact superdense coding, but not for exact teleportation.

Research paper thumbnail of Wigner's approach enabled detection of genuine multipartite nonlocality and its finer characterisation using all different bipartitions

Cornell University - arXiv, Feb 23, 2022

Research paper thumbnail of Resource state structure for cooperative quantum key distribution

Quantum entanglement plays a pivotal role in a number of communication protocols, like secret sha... more Quantum entanglement plays a pivotal role in a number of communication protocols, like secret sharing and quantum cryptography. We consider a scenario where more than two parties are involved in a protocol and they share a multipartite entangled state. In particular, we introduce the protocol of cooperative quantum key distribution (CoQKD). In this protocol, two parties, Alice and Bob establish a key with the cooperation of other parties. Other parties control whether Alice and Bob can establish the key, its security and the key rate. We discuss the case of three parties in detail and find the necessary suitable resource states. We discuss the controlling power of the third party, Charlie. We also examine the usefulness of this new resource state for generating conference key and for cooperative teleportation. In the case of conference key, we find that recently introduced Bell inequalities can be useful to establish the security. We also generalize the scenario to more than three p...

Research paper thumbnail of Resource state structure for controlled quantum key distribution

The European Physical Journal D, 2020

Quantum entanglement plays a pivotal role in many communication protocols, like secret sharing an... more Quantum entanglement plays a pivotal role in many communication protocols, like secret sharing and quantum cryptography. We consider a scenario where more than two parties are involved in a protocol and share a multipartite entangled state. In particular, we considered the protocol of Controlled Quantum Key Distribution (CoQKD), introduced in the Ref. Chin. Phys. Lett. 20, 183-185 (2003), where, two parties, Alice and Bob establish a key with the cooperation of other parties. Other parties control/supervise whether Alice and Bob can establish the key, its security and key rate. We discuss the case of three parties in detail and find suitable resource states. We discuss the controlling power of the third party, Charlie. We also examine the usefulness of the new resource states for generating conference key and for cooperative teleportation. We find that recently introduced Bell inequalities can be useful to establish the security of the conference key. We also generalize the scenario to more than three parties.

Research paper thumbnail of Two-qubit mixed states and teleportation fidelity: purity, concurrence, and beyond

The European Physical Journal D, 2018

To explore the properties of a two-qubit mixed state, we consider quantum teleportation. The fide... more To explore the properties of a two-qubit mixed state, we consider quantum teleportation. The fidelity of a teleported state depends on the resource state purity and entanglement, as characterized by concurrence. Concurrence and purity are functions of state parameters. However, it turns out that a state with larger purity and concurrence, may have comparatively smaller fidelity. By computing teleportation fidelity, concurrence and purity for two-qubit X-states, we show it explicitly. We further show that fidelity changes monotonically with respect to functions of parameters-other than concurrence and purity. A state with smaller concurrence and purity, but larger value of one of these functions has larger fidelity. These functions, thus characterize nonlocal classical and/or quantum properties of the state that are not captured by purity and concurrence alone. In particular, concurrence is not enough to characterize the entanglement properties of a two-qubit mixed state.

Research paper thumbnail of More communication with less entanglement

The European Physical Journal D, 2015

We exhibit the intriguing phenomena of "Less is More" using a set of multipartite entangled state... more We exhibit the intriguing phenomena of "Less is More" using a set of multipartite entangled states. We consider the quantum communication protocols for the exact teleportation, superdense coding, and quantum key distribution. We find that sometimes less entanglement is more useful. To understand this phenomena we obtain a condition that a resource state must satisfy to communicate a n-qubit pure state which has m terms. We find that an appropriate partition of the resource state should have a von-Neumann entropy of log 2 m. Furthermore, it is shown that some states may be suitable for exact superdense coding, but not for exact teleportation.