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Quantum cryptography

Michele Mosca giving a speech

Every time you perform an online transaction, such as a purchase or bank transfer, you entrust your personal data to a secure encryption system. Such encryption is based on mathematical problems too difficult for present-day computers to crack, which is why your information is relatively safe. But future computers — quantum computers in particular — will be able to decrypt many such coded messages. We need new cryptographic tools that are secure in a quantum world. Fortunately, the rules of quantum mechanics enable codes that cannot be broken with any amount of computing power.

The rules of quantum mechanics dictate that a quantum system cannot be observed without being disrupted. This means that “ key” material exchanged via quantum communication will bear the indelible fingerprint of any attempted eavesdropping. Eavesdropped keys can be abandoned, and only truly private keys are kept to be used in unbreakable encryption protocols.

BobThe Institute for Quantum Computing (IQC) is home to Alice, a photon receiver in a Quantum Key Distribution (QKD) system. Alice’s counterpart, Bob, is housed in an office at Waterloo’s Perimeter Institute for Theoretical Physics. Alice and Bob receive entangled (highly correlated) photons emitted from a crystal excited by a laser. By measuring the unique polarization of the photons, Alice and Bob receive random (but identical) “keys” which can be used to encode messages.

IQC researcher Norbert Lütkenhaus is a leading international authority on the security of practical quantum key distribution systems. Thomas Jennewein is a world leader in quantum communication and quantum cryptography in free space. IQC's newest research assistant professor, Vadim Makarov, is a "quantum hacker" whose research focuses on finding the vulnerabilities in hardware implementations of QKD, and recommending solutions. He plays the part of "Eve," the eavesdropper, in communications between Alice and Bob. IQC researchers including Richard Cleve, Raymond Laflamme, Debbie Leung, Michele Mosca and Ashwin Nayak have worked on these and other facets of quantum cryptography, such as quantum fingerprints, quantum money and quantum private channels.

Top left, Michele Mosca. To the right is "Bob", a photon detector used in quantum key distribution.