One of the greatest threats to today’s connected world is the vulnerability of digital communication. Hackers devise ways to steal our identities, money and secrets. Cryptography is the science of secrets, which allows information to be exchanged over long distances, but remain secret from any unintended eavesdroppers. Most modern cryptographic methods rely on problems like factoring, which are difficult for digital computers to solve. The possibility of quantum computers in the future requires us to re-examine how we keep our information secure.
Quantum key distribution (QKD) is a form of cryptography based on the uncertainty principle, and keeps our information absolutely safe, even against an attack from a quantum computer.
QKD is already in use. Several companies sell QKD systems and many governments and private organizations use it for information security. It was even used in 2007 to protect results in a Swiss election.
The goal of QKD is to create a shared secret key between two parties that is perfectly secure. In the simplest version, one party sends qubits in certain quantum states to other party who observes or measures them. Anyone trying to eavesdrop must also measure these qubits, which leaves a detectable trace. This is due to the uncertainty principle, which says you cannot measure a quantum state without disturbing it.
If the qubits have been disturbed, both parties know to abandon the exchange and throw away the key. Otherwise, they can use the key to exchange perfectly secure communication.
Quantum-safe cryptography is a complementary approach to QKD. Quantum computers will have advantages over digital computers for many problems, but not for all. Quantum-safe cryptography focuses on developing new classical cryptographic methods based on mathematical problems believed to be difficult for even quantum computers to solve.
Now don’t get too excited, this doesn't mean we can teleport humans! Quantum teleportation teleports information, not matter. It’s kind of like a quantum fax machine.
Quantum teleportation uses entanglement to transfer the quantum state of a particle onto a different particle. In the process, teleportation destroys the initial quantum state. What is interesting is the quantum state never existed in between the two locations.
Scientists have demonstrated quantum teleportation many times using trapped ions, spins, photons and superconducting qubits. In 2012, a team from Vienna and the University of Waterloo teleported the state of a photon over 143km between two of the Canary Islands.
Teleportation is more than just cool science. Using teleportation is an important part of many quantum computing architectures, where it allows quantum information to be swapped between different qubits.