Kfir Sulimany

We show that the vacuum fluctuations of coherent light can serve as a cryptographic resource for private neural-network inference. A server encodes proprietary model weights into weak coherent states; a client computes the inference optically and returns a certificate state whose excess noise the server verifies. Weight-leakage bounds derived via the Holevo theorem hold against all IID attacks, including non-Gaussian ones. Data-leakage bounds derived via Cramér–Rao inequalities hold against individual attacks with arbitrary probes and collective attacks with Gaussian probes. On MNIST, the protocol achieves >95% accuracy with leakage below 0.1 bits per weight and per data element, an order of magnitude below the precision needed for functional inference. All components are standard CV-QKD hardware. Published in Physical Review X 15, 041056 (2025).

We introduce encoding strategy of k-symbol embeddings within a d-dimensional Hilbert space, validate using d=25 experimental data and determine optimum at k=5. These findings pave the way for error-correction and modulation for quantum cryptography.

We formalize the security proof chain of the BB84 quantum key distribution protocol in Lean 4, an interactive theorem prover. The development covers IID security, collective attacks, the quantum de Finetti theorem, and the reduction from general attacks to collective attacks. Every deduction is verified by the Lean proof kernel, ensuring that all assumptions and preconditions are explicit and mechanically checked. The project also introduces a reusable quantum information theory library supporting entropy inequalities, quantum channels, and representation-theoretic tools required for QKD security proofs. The resulting development establishes a Lean framework for machine-verified quantum cryptographic security proofs.

High-dimensional quantum key distribution (QKD) provides ultimate secure communication with secure key rates that cannot be obtained by QKD protocols with binary encoding. However, so far the proposed protocols required additional experimental resources, thus raising the cost of practical high-dimensional systems and limiting their use. Here, we analyze and demonstrate a novel scheme for fiber-based arbitrary-dimensional QKD, based on the most popular commercial hardware for binary time bins encoding. Quantum state transmission is tested over 40 km channel length of standard single-mode fiber, exhibiting a two-fold enhancement of the secret key rate in comparison to the binary Coherent One Way (COW) protocol, without introducing any hardware modifications. This work holds a great potential to enhance the performance of already installed QKD systems by software update alone.