[Paper Review] Quantum Locker Using a Novel Verification Algorithm and Its Experimental Realization in IBM Quantum Computer

Avinash Dash, Sumit Rout+2 more|arXiv (Cornell University)|Oct 14, 2017

Quantum Information and Cryptography45 references16 citations

TL;DR

This paper proposes a quantum locker protocol that uses a novel weak-measurement-based verification algorithm to deterministically distinguish arbitrary single-qubit superposition states from eigenstates, enabling a secure quantum one-time password (OTP) system. The protocol ensures message retrieval only upon correct verification of a dynamically generated, non-reusable quantum OTP, with experimental validation on IBM Quantum hardware achieving high fidelity.

ABSTRACT

It is well known that Grover's algorithm asymptotically transforms an equal superposition state into an eigenstate (of a given basis). Here, we demonstrate a verification algorithm based on weak measurement which can achieve the same purpose even if the qubit is not in an equal superposition state. The proposed algorithm highlights the distinguishability between any arbitrary single qubit superposition state and an eigenstate. We apply this algorithm to propose the scheme of a Quantum Locker, a protocol in which any legitimate party can verify his/her authenticity by using a newly developed quantum One-Time Password (OTP) and retrieve the necessary message from the locker. We formally explicate the working of quantum locker in association with the quantum OTP, which theoretically offers a much higher security against any adversary, as compared to any classical security device.

Motivation & Objective

• To develop a verification algorithm capable of distinguishing arbitrary superposition states from eigenstates, even when the initial state is unknown and not equally weighted.
• To address the limitation of existing quantum search algorithms that fail when the initial state is not an equal superposition or when coefficients are unknown.
• To design a quantum locker system that leverages quantum one-time passwords (OTP) for secure message retrieval, ensuring information cannot be cloned or replayed.
• To experimentally realize the proposed verification algorithm and quantum locker protocol on the IBM Quantum platform with high fidelity.
• To demonstrate that the protocol prevents message leakage even under adversarial conditions by destroying the OTP after a single use.

Proposed method

• The verification algorithm employs weak measurement on an ancillary qubit to probabilistically collapse an arbitrary superposition state to an eigenstate, with the outcome indicating whether the input is an eigenstate or superposition.
• The protocol uses a controlled-NOT (CNOT) and Toffoli (CCNOT) gate structure to conditionally transfer the message qubit to a blank qubit only if the OTP qubit collapses to |0⟩ after verification.
• The quantum OTP is generated using random parameters (θ₁, θ₂, θ₃) to prepare a single-qubit state |ϕ⟩ = cos(θ₁)|0⟩ + sin(θ₁)e^{iθ₂}|1⟩, which is non-replicable due to the no-cloning theorem.
• The message is encoded in a separate qubit register and transferred to a blank qubit register only when all OTP qubits are verified as |0⟩, using a C^{n+1}NOT gate for n OTP qubits.
• The protocol is implemented on IBM Quantum Experience using real quantum hardware, with fidelity measured via state tomography and comparison with ideal outcomes.
• The verification process is repeated iteratively to amplify the probability of correct eigenstate detection, achieving asymptotic determinism despite the probabilistic nature of weak measurement.

Experimental results

Research questions

• RQ1 Can a quantum verification algorithm distinguish an arbitrary superposition state from an eigenstate without prior knowledge of the state’s amplitudes?
• RQ2 Can such a verification algorithm be used to build a secure, unclonable one-time password system for quantum information retrieval?
• RQ3 How can the probabilistic nature of weak measurement be leveraged to achieve high-fidelity, deterministic verification of quantum OTPs in practice?
• RQ4 What is the experimental feasibility and fidelity of implementing the proposed quantum locker protocol on near-term quantum hardware?
• RQ5 To what extent does the protocol prevent message leakage when an incorrect or non-eigenstate OTP is used?

Key findings

• The proposed verification algorithm successfully distinguishes arbitrary superposition states from eigenstates with high fidelity, even when the initial state is not equally weighted or unknown.
• The algorithm achieves asymptotic determinism in identifying eigenstates through iterative weak measurement, reducing the failure probability to negligible levels.
• The quantum locker protocol enables secure message retrieval only when the correct quantum OTP is provided, with the OTP being destroyed after use, ensuring one-time access.
• Experimental implementation on IBM Quantum hardware demonstrated high state fidelity (close to ideal) in state preparation and verification, validating the protocol’s feasibility.
• The protocol prevents message leakage even when a wrong OTP is entered, due to the verification mechanism ensuring message transfer only upon successful collapse to |0⟩.
• The use of multiple qubits for the OTP (e.g., n=3) enhances security, with the system requiring all OTP qubits to collapse to |0⟩ for message transfer, significantly reducing the chance of unauthorized access.