Zhuang group

Introduction

We are the quantum information theory group at Ming Hsieh Department of Electrical and Computer Engineering of University of Southern California. Our group explores fundamental quantum information theory in connection to communication, sensing and computing applications. We aim to understand the role of quantum resources such as entanglement and squeezing in operational tasks, and the process to establish these quantum resources in a local or distant network setting.

This site has stopped updating and please refer to https://sites.usc.edu/zhuang/ for more updates

Job opportunities

Postdocs in quantum information theory (sensing, communication and computing), please contact qzhuang <at> usc.edu

Graduate students with some quantum background, send me an email at: qzhuang <at> usc.edu

News

July, 2022, "Quantum computational phase transition in combinatorial problems" in collaboration with Akira Sone published in npj Quantum Inf.

Quantum computational phase transition in combinatorial problems - npj Quantum Information

June, 2022, "Demonstration of Entanglement-Enhanced Covert Sensing" in collaboration with Zheshen Zhang group published in Phys. Rev. Lett.

Demonstration of Entanglement-Enhanced Covert SensingThe laws of quantum physics endow superior performance and security for information processing: quantum sensing harnesses nonclassical resources to enable measurement precision unmatched by classical sensing, whereas quantum cryptography aims to unconditionally protect the secrecy of the processed information. Here, we present the theory and experiment for entanglement-enhanced covert sensing, a paradigm that simultaneously offers high measurement precision and data integrity by concealing the probe signal in an ambient noise background so that the execution of the protocol is undetectable with a high probability. We show that entanglement offers a performance boost in estimating the imparted phase by a probed object, as compared to a classical protocol at the same covertness level. The implemented entanglement-enhanced covert sensing protocol operates close to the fundamental quantum limit by virtue of its near-optimum entanglement source and quantum receiver. Our work is expected to create ample opportunities for quantum information processing at unprecedented security and performance levels.

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January 27 2022, PI Zhuang wins the National Science Foundation CAREER Award for the project "Using Entanglement to Enhance Communication and Sensing in the Presence of Noise".

Four University of Arizona Engineering Professors Win NSF CAREER AwardsFour faculty members in the University of Arizona College of Engineering have received CAREER Awards from the National Science Foundation. Their work ranges from improving drug delivery for disease and managing renewable energy to advancing quantum technology. The CAREER Award is the foundation’s most prestigious recognition of early-career faculty with potential to serve as academic role models in research and education.

January 5 2022, "Ultimate Accuracy Limit of Quantum Pulse-Compression Ranging" in collaboration with Jeffrey Shapiro published in Phys. Rev. Lett.
The paper was reported in Phys.org news.

Ultimate Accuracy Limit of Quantum Pulse-Compression RangingRadars use time-of-flight measurement to infer the range to a distant target from its return's round-trip range delay. They typically transmit a high time-bandwidth product waveform and use pulse-compression reception to simultaneously achieve satisfactory range resolution and range accuracy under a peak transmitted-power constraint. Despite the many proposals for quantum radar, none have delineated the ultimate quantum limit on ranging accuracy. We derive that limit through continuous-time quantum analysis and show that quantum illumination ranging---a quantum pulse-compression radar that exploits the entanglement between a high time-bandwidth product transmitted signal pulse and and a high time-bandwidth product retained idler pulse---achieves that limit. We also show that quantum illumination ranging offers mean-squared range-delay accuracy that can be tens of dB better than that of a classical pulse-compression radar of the same pulse bandwidth and transmitted energy.

A new look at quantum radar suggests it might boost accuracy more than thoughtA combined team of researchers from the University of Arizona and MIT reports that quantum radar might be able to boost the accuracy of radar systems more than has been thought. In their paper published in the journal Physical Review Letters, the group describes a new approach to developing quantum radar and the obstacles that stand in the way of its development.

June 22 2021, "Entanglement-Assisted Communication Surpassing the Ultimate Classical Capacity" in collaboration with Zheshen Zhang's group published in Phys. Rev. Lett.

Entanglement-Assisted Communication Surpassing the Ultimate Classical CapacityEntanglement underpins a variety of quantum-enhanced communication, sensing, and computing capabilities. Entanglement-assisted communication (EACOMM) leverages entanglement preshared by communicating parties to boost the rate of classical information transmission. Pioneering theory works showed that EACOMM can enable a communication rate well beyond the ultimate classical capacity of optical communications, but an experimental demonstration of any EACOMM advantage remains elusive. In this Letter we report the implementation of EACOMM surpassing the classical capacity over lossy and noisy bosonic channels. We construct a high-efficiency entanglement source and a phase-conjugate quantum receiver to reap the benefit of preshared entanglement, despite entanglement being broken by channel loss and noise. We show that EACOMM beats the Holevo-Schumacher-Westmoreland capacity of classical communication by up to 16.3%, when both protocols are subject to the same power constraint at the transmitter. As a practical performance benchmark, we implement a classical communication protocol with the identical characteristics for the encoded signal, showing that EACOMM can reduce the bit-error rate by up to 69% over the same bosonic channel. Our work opens a route to provable quantum advantages in a wide range of quantum information processing tasks.

June 14 2021, "Quantum Ranging with Gaussian Entanglement" of our group published in Phys. Rev. Lett..

Quantum Ranging with Gaussian EntanglementIt is well known that entanglement can benefit quantum information processing tasks. Quantum illumination, when first proposed, was surprising as the entanglement's benefit survived entanglement-breaking noise. Since then, many efforts have been devoted to study quantum sensing in noisy scenarios. The applicability of such schemes, however, is limited to a binary quantum hypothesis testing scenario. In terms of target detection, such schemes interrogate a single spatiotemporal resolution bin at a time, limiting the impact to radar detection. We resolve this binary-hypothesis limitation by proposing an entanglement-assisted quantum ranging protocol. By formulating a ranging task as a multiary hypothesis testing problem, we show that entanglement enables a 6-dB advantage in the error exponent against the optimal classical scheme. Moreover, the proposed ranging protocol can also be used to implement a pulse-position modulated entanglement-assisted communication protocol. Our ranging protocol reveals entanglement's potential in general quantum hypothesis testing tasks and paves the way toward a quantum-ranging radar with a provable quantum advantage.

June 1 2021, "Quantum-Enhanced Data Classification with a Variational Entangled Sensor Network" of our group in collaboration with Zheshen Zhang's group published in Phys. Rev. X and featured in Physics. See also reports from UA News.

Quantum-Enhanced Data Classification with a Variational Entangled Sensor NetworkQuantum machine-learning techniques speed up the task of classifying data delivered by a small network of quantum sensors.

May 19 2021, "Entanglement-assisted capacity regions and protocol designs for quantum multiple-access channels" of our group published in npj Quantum Inf.

Entanglement-assisted capacity regions and protocol designs for quantum multiple-access channels

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Feb 16 2021, "Entanglement formation in continuous-variable random quantum networks" of our group published in npj Quantum Inf.

Entanglement formation in continuous-variable random quantum networks

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Feb 10 2021, "Quantum-Enabled Communication without a Phase Reference" of our group published in Phys. Rev. Lett.

Quantum-Enabled Communication without a Phase ReferenceA phase reference has been a standard requirement in continuous-variable quantum sensing and communication protocols. However, maintaining a phase reference is challenging due to environmental fluctuations, preventing quantum phenomena such as entanglement and coherence from being utilized in many scenarios. We show that quantum communication and entanglement-assisted communication without a phase reference are possible, when a short-time memory effect is present. The degradation in the communication rate of classical or quantum information transmission decreases inversely with the correlation time. Exact solutions of the quantum capacity and entanglement-assisted classical and quantum capacity for pure dephasing channels are derived, where non-Gaussian multipartite-entangled states show strict advantages over usual Gaussian sources. For thermal-loss dephasing channels, lower bounds of the capacities are derived. The lower bounds also extend to scenarios with fading effects in the channel. In addition, for entanglement-assisted communication, the lower bounds can be achieved by a simple phase-encoding scheme on two-mode squeezed vacuum sources, when the noise is large.

Oct 28 2020, "Entanglement-Assisted Absorption Spectroscopy" of our group published in Phys. Rev. Lett.

Entanglement-Assisted Absorption SpectroscopySpectroscopy is an important tool for probing the properties of materials, chemicals, and biological samples. We design a practical transmitter-receiver system that exploits entanglement to achieve a provable quantum advantage over all spectroscopic schemes based on classical sources. To probe the absorption spectra, modeled as a pattern of transmissivities among different frequency modes, we employ broadband signal-idler pairs in two-mode squeezed vacuum states. At the receiver side, we apply photodetection after optical parametric amplification. Finally, we perform a maximum likelihood decision test on the measurement results, achieving an error probability orders of magnitude lower than the optimum classical systems in various examples, including ``wine tasting'' and ``drug testing'' where real molecules are considered. In detecting the presence of an absorption line, our quantum scheme achieves the optimum performance allowed by quantum mechanics. The quantum advantage in our system is robust against noise and loss, which makes near-term experimental demonstration possible.

Our team is now involved in two big quantum centers.

UArizona Collaborates on $115M Effort to Build Quantum ComputerThree College of Engineering researchers are involved in the Superconducting Quantum Materials and Systems Center, which is part of a $625 million federal program to foster quantum innovation in the United States.

University of Arizona Awarded $26M to Architect the Quantum InternetThe University of Arizona will receive an initial, five-year, $26 million grant from the National Science Foundation, with an additional five-year $24.6 million option, to establish and lead a new National Science Foundation Engineering Research Center – called the Center for Quantum Networks – with core partners Harvard University, the Massachusetts Institute of Technology and Yale University.

Aug 2020, PI Zhuang is awarded the 2020 DARPA Young Faculty Award (YFA).

DARPA Awards Quntao Zhuang Young Faculty AwardQuntao Zhuang, an assistant professor in the Department of Electrical and Computer Engineering and the James C. Wyant College of Optical Sciences, received a 2020 Young Faculty Award from the U.S. Defense Advanced Research Projects Agency, or DARPA. The award recognizes rising stars in junior research positions whose work can benefit the Department of Defense and issues of national security.

Aug 21 2020, second joint work with Stefano Pirandola is published in Phys. Rev. Lett

Ultimate Limits for Multiple Quantum Channel DiscriminationQuantum hypothesis testing is a central task in the entire field of quantum information theory. Understanding its ultimate limits will give insight into a wide range of quantum protocols and applications, from sensing to communication. Although the limits of hypothesis testing between quantum states have been completely clarified by the pioneering works of Helstrom in the 1970s, the more difficult problem of hypothesis testing with quantum channels, i.e., channel discrimination, is less understood. This is mainly due to the complications coming from the use of input entanglement and the possibility of employing adaptive strategies. In this Letter, we establish a lower limit for the ultimate error probability affecting the discrimination of an arbitrary number of quantum channels. We also show that this lower bound is achievable when the channels have certain symmetries. As an example, we apply our results to the problem of channel position finding, where the goal is to identify the location of a target channel among multiple background channels. In this general setting, we find that the use of entanglement offers a great advantage over strategies without entanglement, with nontrivial implications for data readout, target detection, and quantum spectroscopy.

June 2 2020, recent work with Stefano Pirandola is published in Commun. Phys.

Entanglement-enhanced testing of multiple quantum hypothesesQuantum channel discrimination exploits quantum resources to improve hypothesis testing for binary bosonic channels. Here, the authors overcome the binary setting, showing quantum entanglement greatly enhances the discrimination performance for an arbitrary number of channels.

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April 17 2020, Our recent work in collaboration with Zheshen Zhang's group is published in Phys. Rev. Lett.

Demonstration of a Reconfigurable Entangled Radio-Frequency Photonic Sensor Network

Quantum Entanglement Offers Unprecedented Precision for GPS and More

Quantum entanglement offers unprecedented precision for GPS and more (Update)

March 11, 2020, our paper "Practical Route to Entanglement-Assisted Communication Over Noisy Bosonic Channels" is published in Phys. Rev. Applied.

Practical Route to Entanglement-Assisted Communication Over Noisy Bosonic ChannelsEntanglement offers substantial advantages in quantum information processing, but loss and noise hinder its application in practical scenarios. Although it has been well known for decades that the classical communication capacity of lossy and noisy bosonic channels can be significantly enhanced by entanglement, no practical encoding and decoding schemes are available to realize any entanglement-enabled advantage. Here, we report structured encoding and decoding schemes for such an entanglement-assisted communication scenario. Specifically, we show that phase encoding on an entangled two-mode squeezed vacuum state saturates the entanglement-assisted classical communication capacity of a very noisy channel and overcomes the fundamental limit on covert communication that exists without the assistance of entanglement. We then construct receivers for optimum hypothesis-testing protocols with discrete phase modulation and for optimum noisy phase-estimation protocols with continuous phase modulation. Our results pave the way for entanglement-assisted communication and sensing in the radio-frequency and microwave spectral ranges.

Feb 27 2020, our paper "Distributed quantum sensing enhanced by continuous-variable error correction" is published in New J. Phys. as the one-millionth article of IOP publishing.

IOP Publishing celebrates one millionth article (and counting) - IOP PublishingIOP Publishing celebrates one millionth article (and counting) 27 Feb 2020 Simon Davies Millionth article is published in New Journal of Physics, the pioneering open access journal launched by the Institute of Physics and the Deutsche Physikalische Gesellschaft Milestone is reached as 150,000 archive articles from The Electrochemical Society are added to IOPscience IOP...

October 31 2019, our paper "Physical-Layer Supervised Learning Assisted by an Entangled Sensor Network" is published in Phys. Rev. X.

Physical-Layer Supervised Learning Assisted by an Entangled Sensor NetworkA new paradigm for performing machine learning tasks on a quantum processor offers a potential boost to sensing applications using readily available quantum devices and components.