Room 117

Bound Entangled States with a Private Key and their Classical Counterpart

Krishnakumar Sabapathy

IMSc

Entanglement is a fundamental resource for quantum information
processing. In its pure form, it allows quantum teleportation and sharing
classical secrets. Realistic quantum states are noisy and their usefulness
is only partially understood. Bound-entangled states are central to this
question—they have no distillable entanglement, yet sometimes still have a
private classical key. We present a construction of bound-entangled states
with a private key based on classical probability distributions. From this
emerge states possessing a new classical analogue of bound entanglement,
distinct from the long-sought bound information. We also find states of
smaller dimensions and higher key rates than previously known. Our
construction has implications for classical cryptography: we show that
existing protocols are insufficient for extracting private key from our
distributions due to their “bound-entangled” nature. We propose a simple
extension of existing protocols that can extract a key from them.

Link: journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.110502

Supp. Material:
journals.aps.org/prl/supplemental/10.1103/PhysRevLett.112.110502/PRL_appendix.pdf