By combining quantum computing with quantum cryptography, a perfectly secure cloud computing environment was achieved, addressing one of the many challenges facing the current trend of storing information remotely. Clusters of entangled qubits allow remote quantum computing to be performed on a server while the contents and results are kept hidden from the remote server. (Images: Equinox Graphics) Quantum computers are expected to play an important role in future information processing since they can outperform classical computers at many tasks. Considering the challenges inherent in building quantum devices, it is conceivable that future quantum computing capabilities will exist only in a few specialized facilities around the world — much as with today’s supercomputers. Users could interact with these specialized facilities to outsource their quantum computations, similar to the cloud computing trend. To answer the challenge, researchers at the University of Vienna have demonstrated that perfectly secure cloud computing can be achieved using the principles of quantum mechanics. “Quantum physics solves one of the key challenges in distributed computing,” said Stefanie Barz, lead author of the study. “It can preserve data privacy when users interact with remote computing centers.” The researchers performed an experimental demonstration of quantum computation in which the input, the data processing and the output remained unknown to the quantum computer. Dubbed “blind quantum computing,” it was the first known successful quantum computation during which the user’s data stayed perfectly encrypted. This particular experiment used photons to encrypt the data because they are compatible with quantum computations and can travel over long distances. Multiple superimposed strings of data are encoded in such a way that the quantum computation can be performed on a remote server, while still securely encrypted. The process begins when a user prepares qubits in a state known only to himself and sends them to the quantum computer. The quantum server entangles the qubits using a standard scheme. The actual computation is measurement-based: The processing of quantum information is implemented by simple measurements on qubits. The user tailors measurement instructions to the particular state of each qubit and sends them to the quantum server. Finally, the qubits are sent back to the user, who can interpret and utilize the results of the computation. The scientists say that even if the quantum computer or a hacker tries to read the qubits, they are “blind” because they cannot gain access to any information without knowing the data’s initial state. The experiment, which was carried out at the Vienna Center for Quantum Science and Technology at the University of Vienna and at the Institute for Quantum Optics and Quantum Information, appears in the Jan. 20 issue of Science. For more information, visit: www.univie.ac.at