About

Tim Byrnes is an Associate Professor of Physics at NYU Shanghai and a Visiting Assistant Professor at the National Institute of Informatics in Tokyo, Japan. He holds a PhD from the University of New South Wales in Sydney, Australia, where he specialized in condensed matter physics and high energy physics under the supervision of Prof. Chris Hamer. His research interests encompass quantum information technologies, condensed matter physics, and atomic, molecular, optical (AMO) physics. Specifically, he investigates applications of Bose-Einstein condensates to quantum information, exploring their potential in quantum computation and simulation. Byrnes has also shown interest in the interface of physics and biology, as well as emergent phenomena. His work includes the theory of Bose-Einstein condensation in exciton-polariton systems, the BEC-BCS crossover, and the generation of non-classical light. His academic background includes work on lattice gauge theories using DMRG methods and quantum simulation techniques for solving lattice gauge theories on quantum computers. Byrnes has contributed to the understanding of macroscopic quantum computation, exciton-polariton condensates, and quantum simulators for the Hubbard model with long-range Coulomb interactions.

Research topics

• Physics
• Computer Science
• Quantum mechanics
• Theoretical computer science
• Statistical physics
• Mathematics
• Algorithm

Selected publications

• Quantum teleportation of cat states with binary-outcome measurements

  Quantum Science and Technology · 2025-07-29

  preprintOpen accessSenior author

  Abstract We propose a teleportation protocol involving beam splitting operations and binary-outcome measurements, such as parity measurements. These operations have a straightforward implementation using the dispersive regime of the Jaynes–Cummings Hamiltonian, making our protocol suitable for a broad class of platforms, including trapped ions, circuit quantum electrodynamics and acoustodynamics systems. In these platforms homodyne measurements of the bosonic modes are less natural than dispersive measurements, making standard continuous variable teleportation unsuitable. In our protocol, Alice is in possession of two bosonic modes and Bob a single mode. An entangled mode pair between Alice and Bob is created by performing a beam splitter operation on a cat state. An unknown qubit state encoded by cat states is then teleported from Alice to Bob after a beamsplitting operation, measurement sequence, and a conditional correction. In the case of multiple measurements, near-perfect fidelity can be obtained. We discuss the optimal parameters in order to maximize the fidelity under a variety of scenarios.

  PublisherOA PDFDOI

• Simple determination of dark states in a general multi-level system

  Journal of Physics A Mathematical and Theoretical · 2025-02-18

  articleSenior author

  Abstract In a multi-level energy system with energy transitions, dark states are eigenstates of a Hamiltonian that consist entirely of ground states, with zero amplitude in the excited states. We present several criteria which allows one to deduce the presence of dark states in a general multi-level system based on the submatrices of the Hamiltonian. The dark states can be shown to be the right-singular vectors of the submatrix that connect the ground states to the excited states. Furthermore, we show a simple way of finding the dark state involving the determinant of a matrix constructed from the same submatrix.

  PublisherDOI

• Quantum Repeater Protocol for Deterministic Distribution of Macroscopic Entanglement

  Advanced Quantum Technologies · 2025-02-06 · 2 citations

  articleSenior author

  Abstract Distributing long‐distance entanglement is a fundamental goal that is necessary for a variety of tasks such as quantum communication, distributed quantum computing, and quantum metrology. Currently quantum repeater schemes typically aim to distribute one ebit at a time, the equivalent of one Bell pair's worth of entanglement. Here, a scheme is presented to distribute a macroscopic amount of entanglement across long‐distances using a number of operations that scales only linearly with the chain length in the ideal case (without decoherence). The scheme involves ensembles of qubits and entangling them with an interaction, which can be realized using atomic gas ensembles coupled by a shared optical mode. Using only local measurements on the intermediate ensembles, this leaves the ensembles at the ends of the chain entangled. It is showed that there are particular “magic” interaction times that allow for distribution of entanglement with perfect fidelity, with no degradation with chain length. The scheme is deterministic, such that with suitable local conditional unitary corrections, the same entangled state can always be prepared with good approximation.

  PublisherDOI

• Distillation of supersinglet states

  ArXiv.org · 2025-09-25

  preprintOpen accessSenior author

  We introduce an entanglement distillation (purification) protocol for supersinglet states composed of N qubits. The supersinglet state we target is a total spin zero state with zero spin variance, and has a fully entangled structure involving all qubits. In our distillation protocol, three copies of an initial spin zero state are measured in the local total spin basis such that a higher fidelity supersinglet state is generated upon postselection. The initial state can be prepared using conventional Bell state distillation methods distributed in a way to target the supersinglet symmetries. The protocol uses only local operations and classical communications, and is suitable for long-distance applications such as quantum clock synchronization and cryptography, and avoids a high dimensional Schur transform such that it can be used for tasks such as quantum metrology.

  PublisherOA PDFDOI

• Experimental determination of tripartite quantum discord

  Proceedings of the National Academy of Sciences · 2025-07-02 · 2 citations

  articleOpen accessCorresponding

  Quantum discord is a measure of nonclassical correlations in quantum systems. While the bipartite version of quantum discord is experimentally well-studied, the multipartite version has never been convincingly measured. In this study, we experimentally investigate tripartite quantum discord using an NMR quantum information processor. Building on a theoretical framework for conditional projective measurements and quantum conditional mutual information, we quantify the tripartite quantum discord and its contributions in different three-qubit states such as the Greenberger-Horne-Zeilinger (GHZ) and Werner (W) states as well as classical mixtures of biseparable Bell states, and classical mixtures of product states. The experiments employed full quantum state tomography and temporal averaging to prepare mixed states, achieving fidelities exceeding 95%. Our results confirm that quantum discord persists even in the absence of entanglement, highlighting its utility as a broader indicator of quantum correlations. Furthermore, we validate the nonconvexity of discord, confirming that classical mixtures of zero-discord states can exhibit nonzero discord. This experimentally confirms that quantum discord does not fit into the framework of resource theory. This work establishes a robust methodology for measuring quantum discord, illuminating the structure and distribution of quantum correlations in multipartite systems.

  PublisherDOI

• Pre-emptive parametric kill switch for evaporative atomic sources in vacuum

  ArXiv.org · 2025-10-31

  preprintOpen access

  A robust pre-emptive kill switch for cold atom experiments is introduced to significantly reduce costly system reassembly or replacement. The design incorporates upper (alarm) and lower (evaporation) event detection mechanisms based on predefined thresholds. Meanwhile, a duty cycle timing methodology is used to avert unintentional activation of the dispenser in circumstances where pulse signals occur. The circuit employs generic components, a modular design, and formalized logic, ensuring cost-effectiveness, making the design suitable for school laboratories and other research environments. This design is highly versatile and can be applied to other sensitive devices beyond dispensers, such as heating filaments, titanium sublimation pumps, tungsten lamps, and comparable systems.

  PublisherOA PDFDOI

• Ultrahigh threshold nonstabilizer nonlinear quantum error correcting code

  ArXiv.org · 2025-06-12

  preprintOpen accessSenior author

  We introduce a novel type of quantum error correcting code, called the spinor code, based on spaces defined by total spin. The code is a nonstabilizer code, and is also a nonlinear quantum error correcting code, meaning that quantum information is encoded in a parameterized family of quantum states, rather than a linear superposition of code words. Syndrome measurements are performed by projecting on states with differing total spin, with an associated correction to map states back to the maximum total spin space. We show that the code is asymptotically capable of protecting against any single qubit Pauli error for Gaussian distributed states such as spin coherent state. We directly evaluate the performance under the depolarizing channel, considering various cases, with and without initialization and measurement errors, as well as two qubit errors. We estimate the code-capacity threshold to be in the range of 32-75%, while the phenomenological threshold is in the range 9-75%.

  PublisherOA PDFDOI

• Rényi relative entropy based monogamy of entanglement in tripartite systems

  Scientific Reports · 2025-01-02 · 4 citations

  articleOpen access

  A comprehensive investigation of the entanglement characteristics is carried out on tripartite spin-1/2 systems, examining prototypical tripartite states, the thermal Heisenberg model, and the transverse field Ising model. The entanglement is computed using the Rényi relative entropy. In the traditional Rényi relative entropy, the generalization parameter $$\alpha$$ can take values only in the range $$0 \le \alpha \le 2$$ due to the requirements of joint convexity of the measure. To use the Rényi relative entropy over a wider range of $$\alpha$$ , we use the sandwiched form which is jointly convex in the regime $$0.5 \le \alpha \le \infty$$ . In prototypical tripartite states, we find that GHZ states are monogamous, but surprisingly so are W states. On the other hand, star states exhibit polygamy, due to the higher level of purity of the bipartite subsystems. For spin models, we study the dependence of entanglement on various parameters such as temperature, spin-spin interaction, and anisotropy, and identify regions where entanglement is the largest. The Rényi parameter $$\alpha$$ scales the amount of entanglement in the system. The entanglement measure based on the traditional and the sandwiched Rényi relative entropies obey the Araki-Lieb-Thirring inequality. In the Heisenberg models, namely the XYZ, XXZ, and XY models, the system is always monogamous. However, in the transverse field Ising model, the state is initially polygamous and becomes monogamous with temperature and coupling.

  PublisherOA PDFDOI

• Photon loss effects on light-mediated non-Gaussian entangled Bose–Einstein condensates projecting with different counts

  Physica Scripta · 2025-05-02

  article

  Abstract The theory of quantum information processing for macroscopic qubits is based on the fact that every macroscopic qubit has a conserved number of particles. However, from an experimental point of view, every such qubit experiences decoherence that impacts the possibilities for entanglement generation between such qubits to be used in quantum information processing efficiently. One of the most prospective methods for generating entanglement between distant atomic BECs is quantum nondemolition measurements. Here, we study how the effects of photon measurement impact the entanglement when photon loss decoherence is included. We employ the thermally entangled state representation (TESR) and integral within the ordered operator (IWOP) approach to obtain the accurate density matrix in a photon loss channel. We demonstrate that varying outcomes of photon number measurements lead to the generation of distinct entangled states, each exhibiting unique characteristics. In the scenario where two photoelectric detectors detect the same number of photons n c = n d , we observe that the entangled state demonstrates greater robustness compared to cases with unequal photon counts, providing a reliable resource for better performance with post-processing. We have used Hofmann-Takeuchi and Duan-Giedke-Cirac-Zoller criteria to detect entanglement and find that these methods offer significant benefits in detecting entanglement compared to the Wineland squeezing and EPR steering criteria, when evaluating the regions of detectable entanglement time in these contexts.

  PublisherDOI

• Hybrid quantum-classical unsupervised data clustering based on the self-organizing feature map

  Physical review. A/Physical review, A · 2025-01-09 · 5 citations

  articleOpen access

  Unsupervised machine learning is one of the main techniques employed in artificial intelligence. We introduce an algorithm for quantum-assisted unsupervised data clustering using the self-organizing feature map, a type of artificial neural network. The complexity of our algorithm scales as $O(LN)$, in comparison to the classical case which scales as $O(LMN)$, where $N$ is the number of samples, $M$ is the number of randomly sampled cluster vectors, and $L$ is the number of the shifts of cluster vectors. We perform a proof-of-concept demonstration of one of the central components on the IBM quantum computer and show that it allows us to reduce the number of calculations in the number of clusters. Our algorithm exhibits exponential decrease in the errors of the distance matrix with the number of runs of the algorithm.

  PublisherOA PDFDOI

Frequent coauthors

• Ebubechukwu O. Ilo-Okeke

  168 shared

• Jonathan P. Dowling

  National Institute of Information and Communications Technology

  112 shared

• Valentin Ivannikov

  106 shared

• Y. Yamamoto

  Prefectural University of Hiroshima

  85 shared

• Manikandan Kondappan

  East China Normal University

  79 shared

• Chandrashekar Radhakrishnan

  68 shared

• Manish Chaudhary

  Indian Institute of Science Education and Research Pune

  65 shared

• Alexey N. Pyrkov

  56 shared