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arXiv:1508.07910

Blind Quantum Computing with Decoy States

Xu, Ke, Hoi‐Kwong Lo

Published Aug 31, 2015• 3 citations
arXivHTMLPDF

Abstract

In this paper, we study the Universal Blind Quantum Computing (UBQC) protocol, which allows a client to perform quantum computation on a remote quantum server and the Remote Blind qubit state Preparation (RBSP) protocol which allows the client to prepare single qubits on the server's location with week coherent pulses. This RBSP protocol is inefficient for small $ T $, because the required number of pulses for generating one single qubit scales as $ \mbox{O}(1/T^4) $, where $ T $ is the transmittance of the quantum channe between the client and the server. Our contribution in this paper is a modified RBSP protocol with decoy states. This new protocol allows us to generate $ S $ single qubits simultaneously in a single instance. With our new rotocol, we are able to reduce the number of weak coherent pulses required for generating one single qubit from $ \mbox{O}(1/T^4) $ to nearly $ \mbox{O}(1/T) $, significantly increasing the efficiency. For a 100 km standard telecom fiber of loss 0.2 dB/km, our method gives a six orders of magnitude improvement in the speed, which is very significant.

DOI
10.48550/arxiv.1508.07910

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In this paper, we study the Universal Blind Quantum Computing (UBQC) protocol, which allows a client to perform quantum computation on a remote quantum server and the Remote Blind qubit state Preparation (RBSP) protocol which allows the client to prepare single qubits on the server's location with week coherent pulses. This RBSP protocol is inefficient for small TTT, because the required number of pulses for generating one single qubit scales as \mboxO(1/T4)\mbox{O}(1/T^4)\mboxO(1/T4), where TTT is the transmittance of the quantum channe between the client and the server. Our contribution in this paper is a modified RBSP protocol with decoy states. This new protocol allows us to generate SSS single qubits simultaneously in a single instance. With our new rotocol, we are able to reduce the number of weak coherent pulses required for generating one single qubit from \mboxO(1/T4)\mbox{O}(1/T^4)\mboxO(1/T4) to nearly \mboxO(1/T)\mbox{O}(1/T)\mboxO(1/T), significantly increasing the efficiency. For a 100 km standard telecom fiber of loss 0.2 dB/km, our method gives a six orders of magnitude improvement in the speed, which is very significant.
Quantum computing has seen tremendous progress in past years. Due to implementation complexity and cost, the future path of quantum computation is strongly believed to delegate computational tasks to powerful quantum servers on the cloud. Universal blind quantum computing (UBQC) provides the protocol for the secure delegation of arbitrary quantum computations, and it has received significant attention. However, a great challenge in UBQC is how to transmit a quantum state over a long distance securely and reliably. Here, we solve this challenge by proposing a resource-efficient remote blind qubit preparation (RBQP) protocol, with weak coherent pulses for the client to produce, using a compact and low-cost laser. We experimentally verify a key step of RBQP-quantum nondemolition measurement-in the field test over 100 km of fiber. Our experiment uses a quantum teleportation setup in the telecom wavelength and generates 1000 secure qubits with an average fidelity of (86.9±1.5)%, which exceeds the quantum no-cloning fidelity of equatorial qubit states. The results prove the feasibility of UBQC over long distances, and thus serves as a key milestone towards secure cloud quantum computing.
The universal blind quantum computation (UBQC) protocol [A. Broadbent, J. Fitzsimons, and E. Kashefi, in Proceedings of the 50th Annual IEEE Symposiumon Foundations of Computer Science (IEEE Computer Society, Los Alamitos, CA, USA, 2009), pp. 517-526.] allows a client to perform quantum computation on a remote server. In an ideal setting, perfect privacy is guaranteed if the client is capable of producing specific, randomly chosen single qubit states. While from a theoretical point of view, this may constitute the lowest possible quantum requirement, from a pragmatic point of view, generation of such states to be sent along long distances can never be achieved perfectly. We introduce the concept of ϵ blindness for UBQC, in analogy to the concept of ϵ security developed for other cryptographic protocols, allowing us to characterize the robustness and security properties of the protocol under possible imperfections. We also present a remote blind single qubit preparation protocol with weak coherent pulses for the client to prepare, in a delegated fashion, quantum states arbitrarily close to perfect random single qubit states. This allows us to efficiently achieve ϵ-blind UBQC for any ϵ>0, even if the channel between the client and the server is arbitrarily lossy.
Verifiable blind quantum computing allows a client with poor quantum devices to delegate universal quantum computing to a remote quantum server in such a way that the client's privacy is protected and the honesty of the server is verified. In existing protocols, the client has to send single-qubit states to the server. These states might be decohered by the channel noise. Furthermore, the client hides some "trap" qubits in the server's register so that the client can detect the server's deviation. In reality, however, these trap qubits are disturbed by imperfect operations by the server, which reduces the probability that the client accepts the honest server. To solve these problems, we propose a new gadget that allows the client to remotely prepare encoded logical single-qubit states in the server's place. Importantly, in our fault-tolerant verifiable blind quantum computing protocol, the client needs only the ability of physical single-qubit measurements in XXX and ZZZ bases.
Abstract Blind quantum computation (BQC) allows a client without enough quantum technologies to delegate her quantum computation to a remote quantum server, while keeping her input, output and algorithm secure. In this paper, we propose a universal single-server and almost-classical-client BQC protocol. In this protocol, the client interfaces with only one server and the only ability of the client required is to get particles from the trusted center and forward them to the server. We present an analysis of this protocol and modify it to a universal single-server and fully-classical-client BQC protocol by improving the ability of the trusted center. Based on our protocols and recent works, a new ‘Cloud + Certificate Authority (CA)’ style is proposed for the BQC.
Blind quantum computation (BQC) is a type of quantum computation model. For a client (Alice) who does not have enough sophisticated technology and knowledge to perform universal quantum computation, BQC allows her to resort to a remote quantum computation server (Bob) to delegate universal quantum computation. During the computation, Bob cannot know Alice's inputs, algorithm, and outputs. A single-server BQC protocol requires Alice to prepare and distribute single-photon states to Bob. Unfortunately, the distributed single photons will suffer from noise. The noise not only leads to the decoherence of the single-photon state, but also leads to photon loss. In this protocol, we describe an antinoise single-server BQC protocol. This protocol has three advantages. First, Alice does not require any auxiliary resources, which reduces the client's economic cost. Second, this protocol not only can protect the state from the collective noise, but also can distill the single photon from photon loss. Third, the noise processer in Bob is based on the linear optics so that it is feasible in experiment. This protocol may show that it is possible to perform a single-server BQC protocol in a noise channel.
Blind quantum computation is a scheme that adds unconditional security to cloud quantum computation. In the protocol proposed by Broadbent, Fitzsimons, and Kashefi, the ability to prepare and transmit a single qubit is required for a user (client) who uses a quantum computer remotely. In case a weak coherent pulse is used as a pseudo-single-photon source, however, we must introduce decoy states, owing to the inherent risk of transmitting multiple photons. In this paper, we demonstrate that by using a heralded single-photon source and a probabilistic photon number resolving detector we can gain a higher blind state generation efficiency and longer access distance, owing to noise reduction on account of the heralding signal.