No abstract

With the development of delegated quantum computation, clients will want to ensure confidentiality of their data and algorithms, and the integrity of their computations. While protocols for blind and verifiable quantum computation exist, they suffer from high overheads and from oversensitivity: When running on noisy devices, imperfections trigger the same detection mechanisms as malicious attacks, resulting in perpetually aborted computations. We introduce the first blind and verifiable protocol for delegating BQP computations to a powerful server with repetition as the only overhead. It is composable and statistically secure with exponentially-low bounds and can tolerate a constant amount of global noise.

The application and analysis of the Cut-and-Choose technique in protocols secure against quantum adversaries is not a straightforward transposition of the classical case, among other reasons due to the difficulty to use "rewinding" in the quantum realm. We introduce a Quantum Computation Cut-and-Choose (QC-CC) technique which is a generalisation of the classical Cut-and-Choose in order to build quantum protocols secure against quantum covert adversaries. Such adversaries can essentially deviate arbitrarily provided that their deviation is not detected with high probability. As an application of the QC-CC technique we give a protocol for securely performing a two-party quantum computation with classical input and output. As a basis we use the concept of secure delegated quantum computing [4], and in particular the protocol for quantum garbled circuit computation of [16] that has been proven secure against only a weak specious adversaries (defined in [8]). A unique property of these protocols is the separation between classical and quantum communications and the asymmetry between client and server, which enables us to sidestep the issues linked to quantum rewinding. This opens the possibility of applying the QC-CC technique to other quantum protocols that have this separation. In our proof of security we adapt and use (at different parts of the proof) two quantum rewinding techniques, namely Watrous' oblivious quantum rewinding [27] and Unruh's special quantum rewinding [26]. Our protocol achieves the same functionality as in the previous work on secure two-party quantum computing such as the one in [9], however using the Cut-and-Choose technique on the protocol from [16] leads to the following key improvements: (i) only one-way offline quantum communication is necessary , (ii) only one party (server) needs to have involved quantum technological abilities, (iii) only minimal extra cryptographic primitives are required, namely one oblivious transfer for each input bit and quantumsafe commitments.

We introduce Perceval , an evolutive open-source software platform for simulating and interfacing with discrete-variable photonic quantum computers, and describe its main features and components. Its Python front-end allows photonic circuits to be composed from basic photonic building blocks like photon sources, beam-splitters, phase-shifters and detectors. A variety of computational back-ends are available and optimised for different use-cases. These use state-of-the-art simulation techniques covering both weak simulation, or sampling, and strong simulation. We give examples of Perceval in action by reproducing a variety of photonic experiments and simulating photonic implementations of a range of quantum algorithms, from Grover's and Shor's to examples of quantum machine learning. Perceval is intended to be a useful toolkit both for experimentalists wishing to easily model, design, simulate, or optimise a discrete-variable photonic experiment, and for theoreticians wishing to design algorithms and applications for discrete-variable photonic quantum computing platforms.