Instead of receiving any untrusted quantum system directly from an open quantum channel, a user (say Bob) demands that the state of the system must be converted into classical messages through teleportation (30) right at his doorstep. If Alice and Bob could not afford to receive any untrusted classical message, the whole enterprise of cryptography would be hopeless. Before we present our proof, notice that the assumption that there is no security risk in receiving classical messages is most reasonable because Eve can always send classical messages to Alice and Bob in a “man-in-the-middle” attack during a classical authentication process. As long as there is no security risk for Alice and Bob to receive untrusted classical messages, quantum Trojan horse attack can be foiled. This would certainly make a rigorous proof of security of QKD based on imperfect sources impossible. One might wonder if Eve could perform a quantum Trojan horse attack by hiding robots in (the hidden Hilbert space dimensions of) the quantum systems received by Alice and Bob. Real quantum systems often contain other degrees of freedom that are ignored in quantum computation. This worry is not unfounded because it is notoriously difficult to prepare almost perfect EPR pairs. The real problem is that the Trojan horse pretends to be real EPR pairs when Alice and Bob do their testing but behaves differently when they generate key, thus causing them to leak the information themselves. One might think that this problem could be eliminated by simply shielding the laboratory very well or that such shielding is, in fact, assumed anyway in cryptographic protocols. It is not just that the Trojan horse might leak information once it is in Bob or Alice's laboratory. Smolin has often remarked (41), it is even conceivable that a robot is hidden in the received material and that it pops out to find and disclose secrets to adversaries. Any untrusted material received from an open channel poses serious security risks. This scholarship will be awarded to the first competitive applicant submitting an application.A big worry in cryptography is the Trojan horse attack. The ideal candidate would have an excellent undergraduate record, particularly in quantum theory related courses and would have some research experience in theoretical quantum optics. This joint project between UQ and DTU will combine cutting edge science with the latest quantum optical technology in an international program to realize the next stepping stones towards practical, error corrected quantum channels. The research groups of Prof Ralph at the University of Queensland and Prof Andersen and Dr Neergaard-Nielsen at the Technical University of Denmark (DTU) have pioneered theory and initial demonstrations of such techniques using approaches based on continuous variables. One promising direction is to apply quantum error correction techniques based on linear optics and quantum teleportation to the communication channels. However, distributing quantum states is challenging because of the detrimental decoherence effects caused by transmission through communication channels. The ability to communicate quantum states over long distances is key to numerous quantum technologies of the future such as absolutely secure communications, ultra- precise networks of clocks and distributed quantum computing. You will be associated with UQ as the lead institution, however, you will spend at least 6 months at DTU over the course of your degree. Through the UQ-DTU Joint PhD Supervision Program you can receive a scholarship to study at two leading universities on projects with supervisors from each institution guiding your research. The University of Queensland (UQ) and Denmark Technical University (DTU) have partnered on a Joint PhD Supervision Program to bolster our joint global research impact.
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