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Certified randomness amplification by dynamically probing remote random quantum states
Authors:
Minzhao Liu,
Pradeep Niroula,
Matthew DeCross,
Cameron Foreman,
Wen Yu Kon,
Ignatius William Primaatmaja,
M. S. Allman,
J. P. Campora III,
Akhil Isanaka,
Kartik Singhal,
Omar Amer,
Shouvanik Chakrabarti,
Kaushik Chakraborty,
Samuel F. Cooper,
Robert D. Delaney,
Joan M. Dreiling,
Brian Estey,
Caroline Figgatt,
Cameron Foltz,
John P. Gaebler,
Alex Hall,
Zichang He,
Craig A. Holliman,
Travis S. Humble,
Shih-Han Hung
, et al. (27 additional authors not shown)
Abstract:
Cryptography depends on truly unpredictable numbers, but physical sources emit biased or correlated bits. Quantum mechanics enables the amplification of imperfect randomness into nearly perfect randomness, but prior demonstrations have required physically co-located, loophole-free Bell tests, constraining the feasibility of remote operation. Here we realize certified randomness amplification acros…
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Cryptography depends on truly unpredictable numbers, but physical sources emit biased or correlated bits. Quantum mechanics enables the amplification of imperfect randomness into nearly perfect randomness, but prior demonstrations have required physically co-located, loophole-free Bell tests, constraining the feasibility of remote operation. Here we realize certified randomness amplification across a network by dynamically probing large, entangled quantum states on Quantinuum's 98-qubit Helios trapped-ion quantum processor. Our protocol is secure even if the remote device acts maliciously or is compromised by an intercepting adversary, provided the samples are generated quickly enough to preclude classical simulation of the quantum circuits. We stream quantum gates in real time to the quantum processor, maintain quantum state coherence for $\approx 0.9$ seconds, and then reveal the measurement bases to the quantum processor only milliseconds before measurement. This limits the time for classical spoofing to 30 ms and constrains the location of hypothetical adversaries to a $4{,}500$ km radius. We achieve a fidelity of 0.586 on random circuits with 64 qubits and 276 two-qubit gates, enabling the amplification of realistic imperfect randomness with a low entropy rate into nearly perfect randomness.
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Submitted 5 November, 2025;
originally announced November 2025.
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Quantum-Safe Identity Verification using Relativistic Zero-Knowledge Proof Systems
Authors:
Yao Ma,
Wen Yu Kon,
Jefferson Chu,
Kevin Han Yong Loh,
Kaushik Chakraborty,
Charles Lim
Abstract:
Identity verification is the process of confirming an individual's claimed identity, which is essential in sectors like finance, healthcare, and online services to ensure security and prevent fraud. However, current password/PIN-based identity solutions are susceptible to phishing or skimming attacks, where malicious intermediaries attempt to steal credentials using fake identification portals. Al…
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Identity verification is the process of confirming an individual's claimed identity, which is essential in sectors like finance, healthcare, and online services to ensure security and prevent fraud. However, current password/PIN-based identity solutions are susceptible to phishing or skimming attacks, where malicious intermediaries attempt to steal credentials using fake identification portals. Alikhani et al. [Nature, 2021] began exploring identity verification through graph coloring-based relativistic zero-knowledge proofs (RZKPs), a key cryptographic primitive that enables a prover to demonstrate knowledge of secret credentials to a verifier without disclosing any information about the secret. Our work advances this field and addresses unresolved issues: From an engineering perspective, we relax further the relativistic constraints from 60m to 30m, and significantly enhance the stability and scalability of the experimental demonstration of the 2-prover graph coloring-based RZKP protocol for near-term use cases. At the same time, for long-term security against entangled malicious provers, we propose a modified protocol with comparable computation and communication costs, we establish an upper bound on the soundness parameter for this modified protocol. On the other hand, we extend the two-prover, two-verifier setup to a three-prover configuration, demonstrating the security of such relativistic protocols against entangled malicious provers.
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Submitted 18 July, 2025;
originally announced July 2025.
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Efficient Multi-basis Quantum Position Verification Secure against Generalized Adversaries
Authors:
Wen Yu Kon,
Ignatius William Primaatmaja,
Kaushik Chakraborty,
Charles Lim
Abstract:
Quantum position verification (QPV) enables multiple verifiers to certify a prover's location using quantum communication and physical assumptions. With experimental demonstrations of QPV becoming increasingly feasible, enhancing the practicality and security of QPV protocols is more important than ever. In this work, we make three key contributions toward this goal. First, we introduce a robust Q…
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Quantum position verification (QPV) enables multiple verifiers to certify a prover's location using quantum communication and physical assumptions. With experimental demonstrations of QPV becoming increasingly feasible, enhancing the practicality and security of QPV protocols is more important than ever. In this work, we make three key contributions toward this goal. First, we introduce a robust QPV protocol in which the verifier's state preparation is independent of channel loss, improving reliability in real-world conditions. Second, we refine existing security analysis techniques to bolster protocol resilience against experimental imperfections. Third, we identify and address some implicit assumptions present in existing security analyses, providing a framework to eliminate such assumptions. Additionally, as an example of QPV application beyond location verification, we illustrate how QPV can be leveraged for authenticating classical communication in quantum key distribution.
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Submitted 16 July, 2026; v1 submitted 4 June, 2025;
originally announced June 2025.
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Certified randomness using a trapped-ion quantum processor
Authors:
Minzhao Liu,
Ruslan Shaydulin,
Pradeep Niroula,
Matthew DeCross,
Shih-Han Hung,
Wen Yu Kon,
Enrique Cervero-Martín,
Kaushik Chakraborty,
Omar Amer,
Scott Aaronson,
Atithi Acharya,
Yuri Alexeev,
K. Jordan Berg,
Shouvanik Chakrabarti,
Florian J. Curchod,
Joan M. Dreiling,
Neal Erickson,
Cameron Foltz,
Michael Foss-Feig,
David Hayes,
Travis S. Humble,
Niraj Kumar,
Jeffrey Larson,
Danylo Lykov,
Michael Mills
, et al. (7 additional authors not shown)
Abstract:
While quantum computers have the potential to perform a wide range of practically important tasks beyond the capabilities of classical computers, realizing this potential remains a challenge. One such task is to use an untrusted remote device to generate random bits that can be certified to contain a certain amount of entropy. Certified randomness has many applications but is fundamentally impossi…
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While quantum computers have the potential to perform a wide range of practically important tasks beyond the capabilities of classical computers, realizing this potential remains a challenge. One such task is to use an untrusted remote device to generate random bits that can be certified to contain a certain amount of entropy. Certified randomness has many applications but is fundamentally impossible to achieve solely by classical computation. In this work, we demonstrate the generation of certifiably random bits using the 56-qubit Quantinuum H2-1 trapped-ion quantum computer accessed over the internet. Our protocol leverages the classical hardness of recent random circuit sampling demonstrations: a client generates quantum "challenge" circuits using a small randomness seed, sends them to an untrusted quantum server to execute, and verifies the server's results. We analyze the security of our protocol against a restricted class of realistic near-term adversaries. Using classical verification with measured combined sustained performance of $1.1\times10^{18}$ floating-point operations per second across multiple supercomputers, we certify $71,313$ bits of entropy under this restricted adversary and additional assumptions. Our results demonstrate a step towards the practical applicability of today's quantum computers.
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Submitted 26 March, 2025;
originally announced March 2025.
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Quantum Authenticated Key Expansion with Key Recycling
Authors:
Wen Yu Kon,
Jefferson Chu,
Kevin Han Yong Loh,
Obada Alia,
Omar Amer,
Marco Pistoia,
Kaushik Chakraborty,
Charles Lim
Abstract:
Data privacy and authentication are two main security requirements for remote access and cloud services. While QKD has been explored to address data privacy concerns, oftentimes its use is separate from the client authentication protocol despite implicitly providing authentication. Here, we present a quantum authentication key expansion (QAKE) protocol that (1) integrates both authentication and k…
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Data privacy and authentication are two main security requirements for remote access and cloud services. While QKD has been explored to address data privacy concerns, oftentimes its use is separate from the client authentication protocol despite implicitly providing authentication. Here, we present a quantum authentication key expansion (QAKE) protocol that (1) integrates both authentication and key expansion within a single protocol, and (2) provides key recycling property -- allowing all authentication keys to be reused. We analyse the security of the protocol in a QAKE framework adapted from a classical authentication key exchange (AKE) framework, providing separate security conditions for authentication and data privacy. An experimental implementation of the protocol, with appropriate post-selection, was performed to demonstrate its feasibility.
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Submitted 24 September, 2024;
originally announced September 2024.
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On the Relativistic Zero Knowledge Quantum Proofs of Knowledge
Authors:
Kaiyan Shi,
Kaushik Chakraborty,
Wen Yu Kon,
Omar Amer,
Marco Pistoia,
Charles Lim
Abstract:
We initiate the study of relativistic zero-knowledge quantum proof of knowledge systems with classical communication, formally defining a number of useful concepts and constructing appropriate knowledge extractors for all the existing protocols in the relativistic setting which satisfy a weaker variant of the special soundness property due to Unruh (EUROCRYPT 2012). We show that there exists quant…
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We initiate the study of relativistic zero-knowledge quantum proof of knowledge systems with classical communication, formally defining a number of useful concepts and constructing appropriate knowledge extractors for all the existing protocols in the relativistic setting which satisfy a weaker variant of the special soundness property due to Unruh (EUROCRYPT 2012). We show that there exists quantum proofs of knowledge with knowledge error 1/2 + negl(η) for all relations in NP via a construction of such a system for the Hamiltonian cycle relation using a general relativistic commitment scheme exhibiting the fairly-binding property due to Fehr and Fillinger (EUROCRYPT 2016). We further show that one can construct quantum proof of knowledge extractors for proof systems which do not exhibit special soundness, and therefore require an extractor to rewind multiple times. We develop a new multi-prover quantum rewinding technique by combining ideas from monogamy of entanglement and gentle measurement lemmas that can break the quantum rewinding barrier. Finally, we prove a new bound on the impact of consecutive measurements and use it to significantly improve the soundness bound of some existing relativistic zero knowledge proof systems, such as the one due to Chailloux and Leverrier (EUROCRYPT 2017).
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Submitted 17 December, 2024; v1 submitted 5 September, 2024;
originally announced September 2024.
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Discrete-modulated continuous-variable quantum key distribution secure against general attacks
Authors:
Ignatius William Primaatmaja,
Wen Yu Kon,
Charles Lim
Abstract:
In recent years, discrete-modulated continuous-variable quantum key distribution (DM-CV-QKD) has gained traction due to its practical advantages: cost-effectiveness, simple state preparation, and compatibility with existing communication technologies. This work presents a security analysis of DM-CV-QKD against general sequential attacks, including finite-size effects. Remarkably, our proof conside…
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In recent years, discrete-modulated continuous-variable quantum key distribution (DM-CV-QKD) has gained traction due to its practical advantages: cost-effectiveness, simple state preparation, and compatibility with existing communication technologies. This work presents a security analysis of DM-CV-QKD against general sequential attacks, including finite-size effects. Remarkably, our proof considers attacks that are neither independent nor identical, and makes no assumptions about the Hilbert space dimension of the receiver. To analyse the security, we leverage the recent generalised entropy accumulation theorem and the numerical methods based on quasi-relative entropy. We also develop a novel dimension reduction technique which is compatible with the entropy accumulation framework. While our analysis reveals significant finite-size corrections to the key rate, the protocol might still offer advantages in specific scenarios due to its practical merits. Our work also offers some insights on how future security proofs can improve the security bounds derived in this work.
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Submitted 19 October, 2024; v1 submitted 4 September, 2024;
originally announced September 2024.
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Sampled sub-block hashing for large input randomness extraction
Authors:
Hong Jie Ng,
Wen Yu Kon,
Ignatius William Primaatmaja,
Chao Wang,
Charles Lim
Abstract:
Randomness extraction is an essential post-processing step in practical quantum cryptography systems. When statistical fluctuations are taken into consideration, the requirement of large input data size could heavily penalise the speed and resource consumption of the randomness extraction process, thereby limiting the overall system performance. In this work, we propose a sampled sub-block hashing…
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Randomness extraction is an essential post-processing step in practical quantum cryptography systems. When statistical fluctuations are taken into consideration, the requirement of large input data size could heavily penalise the speed and resource consumption of the randomness extraction process, thereby limiting the overall system performance. In this work, we propose a sampled sub-block hashing approach to circumvent this problem by randomly dividing the large input block into multiple sub-blocks and processing them individually. Through simulations and experiments, we demonstrate that our method achieves an order-of-magnitude improvement in system throughput while keeping the resource utilisation low. Furthermore, our proposed approach is applicable to a generic class of quantum cryptographic protocols that satisfy the generalised entropy accumulation framework, presenting a highly promising and general solution for high-speed post-processing in quantum cryptographic applications such as quantum key distribution and quantum random number generation.
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Submitted 5 August, 2023;
originally announced August 2023.
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Experimental symmetric private information retrieval with measurement-device-independent quantum network
Authors:
Chao Wang,
Wen Yu Kon,
Hong Jie Ng,
Charles C. -W. Lim
Abstract:
Secure information retrieval is an essential task in today's highly digitised society. In some applications, it may be necessary that user query's privacy and database content's security are enforced. For these settings, symmetric private information retrieval (SPIR) could be employed, but its implementation is known to be demanding, requiring a private key-exchange network as the base layer. Here…
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Secure information retrieval is an essential task in today's highly digitised society. In some applications, it may be necessary that user query's privacy and database content's security are enforced. For these settings, symmetric private information retrieval (SPIR) could be employed, but its implementation is known to be demanding, requiring a private key-exchange network as the base layer. Here, we report for the first time a realisation of provably-secure SPIR supported by a quantum-secure key-exchange network. The SPIR scheme looks at biometric security, offering secure retrieval of 582-byte fingerprint files from a database with 800 entries. Our experimental results clearly demonstrate the feasibility of SPIR with quantum secure communications, thereby opening up new possibilities in secure distributed data storage and cloud computing over the future Quantum Internet.
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Submitted 5 October, 2021; v1 submitted 27 September, 2021;
originally announced September 2021.
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Estimating the photon-number distribution of photonic channels with realistic devices and applications in photonic quantum information processing
Authors:
Emilien Lavie,
Ignatius William Primaatmaja,
Wen Yu Kon,
Chao Wang,
Charles Ci Wen Lim
Abstract:
Characterising the input-output photon-number distribution of an unknown optical quantum channel is an important task for many applications in quantum information processing. Ideally, this would require deterministic photon-number sources and photon-number-resolving detectors, but these technologies are still work-in-progress. In this work, we propose a general method to rigorously bound the input…
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Characterising the input-output photon-number distribution of an unknown optical quantum channel is an important task for many applications in quantum information processing. Ideally, this would require deterministic photon-number sources and photon-number-resolving detectors, but these technologies are still work-in-progress. In this work, we propose a general method to rigorously bound the input-output photon number distribution of an unknown optical channel using standard optical devices such as coherent light sources and non-photon-number-resolving detectors/homodyne detectors. To demonstrate the broad utility of our method, we consider the security analysis of practical quantum key distribution systems based on calibrated single-photon detectors and an experimental proposal to implement time-correlated single photon counting technology using homodyne detectors instead of single-photon detectors.
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Submitted 10 September, 2021; v1 submitted 16 February, 2021;
originally announced February 2021.
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Provably-secure symmetric private information retrieval with quantum cryptography
Authors:
Wen Yu Kon,
Charles Ci Wen Lim
Abstract:
Private information retrieval (PIR) is a database query protocol that provides user privacy, in that the user can learn a particular entry of the database of his interest but his query would be hidden from the data centre. Symmetric private information retrieval (SPIR) takes PIR further by additionally offering database privacy, where the user cannot learn any additional entries of the database. U…
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Private information retrieval (PIR) is a database query protocol that provides user privacy, in that the user can learn a particular entry of the database of his interest but his query would be hidden from the data centre. Symmetric private information retrieval (SPIR) takes PIR further by additionally offering database privacy, where the user cannot learn any additional entries of the database. Unconditionally secure SPIR solutions with multiple databases are known classically, but are unrealistic because they require long shared secret keys between the parties for secure communication and shared randomness in the protocol. Here, we propose using quantum key distribution (QKD) instead for a practical implementation, which can realise both the secure communication and shared randomness requirements. We prove that QKD maintains the security of the SPIR protocol and that it is also secure against any external eavesdropper. We also show how such a classical-quantum system could be implemented practically, using the example of a two-database SPIR protocol with keys generated by measurement device-independent QKD. Through key rate calculations, we show that such an implementation is feasible at the metropolitan level with current QKD technology.
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Submitted 17 January, 2021; v1 submitted 28 April, 2020;
originally announced April 2020.
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Non-classicality of spin structures in condensed matter: An analysis of Sr$_{14}$Cu$_{24}$O$_{41}$
Authors:
W. Y. Kon,
T. Krisnanda,
P. Sengupta,
T. Paterek
Abstract:
When two quantum systems are coupled via a mediator, their dynamics has traces of non-classical properties of the mediator. We show how this observation can be effectively utilised to study the quantum nature of materials without well-established structure. A concrete example considered is Sr$_{14}$Cu$_{24}$O$_{41}$. Measurements of low temperature magnetic and thermal properties of this compound…
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When two quantum systems are coupled via a mediator, their dynamics has traces of non-classical properties of the mediator. We show how this observation can be effectively utilised to study the quantum nature of materials without well-established structure. A concrete example considered is Sr$_{14}$Cu$_{24}$O$_{41}$. Measurements of low temperature magnetic and thermal properties of this compound were explained with long-range coupling of unpaired spins through dimerised spin chains. We first show that the required coupling is not provided by the spin chain alone and give alternative compact two-dimensional spin structures compatible with the experimental results. Then we argue that any mediator between the unpaired spins must share with them quantum correlations in the form of quantum discord and in many cases quantum entanglement. In conclusion, present data witnesses quantum mediators between unpaired spins in Sr$_{14}$Cu$_{24}$O$_{41}$.
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Submitted 2 December, 2019; v1 submitted 13 July, 2019;
originally announced July 2019.
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High-intensity two-frequency photoassociation spectroscopy of a weakly bound molecular state: theory and experiment
Authors:
W. Y. Kon,
J. A. Aman,
J. C. Hill,
T. C. Killian,
Kaden R. A. Hazzard
Abstract:
We investigate two-frequency photoassociation of a weakly bound molecular state, focusing on a regime where the ac Stark shift is comparable to the halo-state energy. In this "high-intensity" regime, we observe features absent in low-intensity two-frequency photoassociation. We experimentally measure the spectra of $^{86}$Sr atoms coupled to the least bound state of the $^{86}$Sr$_2$ ground electr…
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We investigate two-frequency photoassociation of a weakly bound molecular state, focusing on a regime where the ac Stark shift is comparable to the halo-state energy. In this "high-intensity" regime, we observe features absent in low-intensity two-frequency photoassociation. We experimentally measure the spectra of $^{86}$Sr atoms coupled to the least bound state of the $^{86}$Sr$_2$ ground electronic channel through an intermediate electronically excited molecular state. We compare the spectra to a simple three-level model that includes a two-frequency drive on each leg of the transition. With numerical solution of the time-dependent Schrodinger equation, we show that this model accurately captures (1) the existence of experimentally observed satellite peaks that arise from nonlinear processes, (2) the locations of the two-photon peak in the spectrum, including ac Stark shifts, and (3) in some cases, spectral lineshapes. To better understand these numerical results, we develop an approximate treatment of this model, based on Floquet and perturbation theory, that gives simple formulas that accurately capture the halo-state energies. We expect these expressions to be valuable tools to analyze and guide future two-frequency photoassociation experiments.
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Submitted 15 July, 2019; v1 submitted 30 December, 2018;
originally announced December 2018.