arXiv subjects

Tzula B. Propp

Publications and source records attributed to Tzula B. Propp.

11 recordsLinked to original sources

arXiv2026

Remotely Preparing Many Qubits with a Single Photon

A single photon in a superposition of $d$ modes naturally encode a $d$-dimensional quantum system, a so-called qudit. We show that such superpositions can be leveraged to achieve a quantum speed-up of remote remote state preparation (RSP): a primitive for several quantum network protocols. For a superposition over $d\geq 2$ modes, the photon state can encode up to ${\rm Log}_2(d)$ qubits, which we exploit in a proposed reflection based RSP protocol with multiple variations. For single qubit RSP, we achieve a performance comparable to the best known existing schemes but with reduced requirements for phase stabilization. For many qubit RSP the achievable success rates remain high despite needing exponentially many temporal modes, since only one photon needs to be transmitted and detected to prepare multiple qubits. By simultaneously preparing many qubits at once, we bypass limited qubit lifetimes limited qubit lifetimes and improve fidelities beyond what is achievable with existing RSP protocols.

quant-ph↗

arXiv2026

Meeting the Needs of the Global Quantum Science Community: A Call to Action

2025 marks one hundred years since the discovery of quantum mechanics. In the century since then, quantum science has blossomed into a global community composed of academics, engineers, developers, and entrepreneurs. The world is currently in the middle of the so-called second quantum revolution, with increased public awareness of quantum science and technology, and growing investment in both quantum hardware and software applications. However, representation remains low among historically marginalized groups: women, LGBTQ+, BIPOC, and people from the global south make up disproportionately few physicists. There are numerous efforts to improve diversity within quantum science, including through workforce development. But many of the changes enacted at the highest levels have failed to result in real change, as highlighted and discussed in the recent Women For Quantum Manifesto of Values. Here, we seek to echo and amplify the need for real change in the quantum ecosystem, emphasizing intersectionality and a feminist approach that centers the most vulnerable members of the quantum community: young students and researchers, especially those communities historically marginalized from quantum science. This report is our attempt to help quantum communities meet this need; we have conducted a survey of quantum scientists all over the world, and here we include both a preliminary report of our findings and policy suggestions we have built to address them. The primary results of our survey are that, 1) marginalized quantum scientists are experiencing hardships and challenges more than their more privileged peers across all metrics, 2) that this fact is hurting retention of diverse, talented quantum scientists in our field, and 3) quantum EDI is an investment in talent retention and resilience building, which are essential for a thriving, globally competitive quantum ecosystem.

physics.soc-ph↗

arXiv2025

Quantum Strategies to Overcome Classical Multiplexing Limits

Near-term quantum networks face a bottleneck due to low quantum communication rates. This degrades performance both by lowering operating speeds and increasing qubit storage time in noisy memories, making some quantum internet applications infeasible. One way to circumvent this bottleneck is multiplexing: combining multiple signals into a single signal to improve the overall rate. Standard multiplexing techniques are classical in that they do not make use of coherence between quantum channels nor account for decoherence rates that vary during a protocol's execution. In this paper, we first derive semiclassical limits to multiplexing for many-qubit protocols, and then introduce two techniques: single click quantum multiplexing and multi-server multiplexing. These can enable beyond-classical multiplexing advantages. We illustrate these techniques through three example applications: 1) entanglement generation between two asymetric quantum network nodes (i.e., repeaters or quantum servers with inequal memories), 2) remote state preparation between many end user devices and a single quantum node, and 3) remote state preparation between one end user device and many internetworked quantum nodes. By utilizing many noisy internetworked quantum devices instead of fewer low-noise devices, our multiplexing strategies enable new paths towards achieving high-speed many-qubit quantum network applications.

quant-ph↗

arXiv2025

Single-click protocols for remote state preparation using weak coherent pulses

Remote state preparation (RSP) allows one party to remotely prepare a known quantum state on another party's qubit using entanglement. This can be used in quantum networks to perform applications such as blind quantum computing or long-distance quantum key distribution (QKD) with quantum repeaters. Devices to perform RSP, referred to as a client, ideally have low hardware requirements, such as only sending photonic qubits. A weak coherent pulse source offers a practical alternative to true single-photon sources and is already widely used in QKD. Here, we introduce two new protocols to the previously known protocol for RSP with a weak-coherent-pulse-based device. The known technique uses a double-click (DC) protocol, where a photon from both the server and the client needs to reach an intermediate Bell state measurement. Here, we add to that a single-click (SC) RSP protocol, which requires only one photon to reach the Bell state measurement, allowing for better performance in certain regimes. In addition, we introduce a double-single-click (DSC) protocol, where the SC protocol is repeated twice, and a CNOT gate is applied between the resulting qubits. DSC mitigates the need for phase stabilization in certain regimes, lowering technical complexity while still improving performance compared to DC in some regimes. We compare these protocols in terms of fidelity and rate, finding that SC consistently achieves higher rates than DC and, interestingly, does not suffer from an inherently lower fidelity than the DC, as is the case for entanglement generation. Although SC provides stronger performance, DSC can still show performance improvements over DC, and it may have reduced technical complexity compared to SC. Lastly, we show how these protocols can be used in long-distance QKD using quantum repeaters.

quant-ph↗

arXiv2024

Decoherence Limits the Cost to Simulate an Anharmonic Oscillator

We study how decoherence increases the efficiency with which we can simulate the quantum dynamics of an anharmonic oscillator, governed by the Kerr effect. As decoherence washes out the fine-grained subPlanck structure associated with phase-space quantum interference in the closed quantum system, open quantum dynamics can be more efficiently simulated using a coarse-grained finite-difference numerical integration. We tie this to the way in which decoherence recovers the semiclassical truncated Wigner approximation (TWA), which strongly differs from the exact closed-system dynamics at times when quantum interference leads to cat states and more general superpositions of coherent states. The regression in quadrature measurement statistics to semiclassical dynamics becomes more pronounced as the initial amplitude of the oscillator grows, with implications for the quantum advantage that might be accessible as system size grows in noisy quantum devices. Lastly, we show that this regression does not have the form of a convex noise model, such as for a depolarizing noise channel. Instead, closed quantum system effects interact with the open system effects, giving rise to distinct open system behavior.

quant-ph↗

arXiv2023

Quantum Computing, Math, and Physics (QCaMP): Introducing quantum computing in high schools

The nascent but rapidly growing field of Quantum Information Science and Technology has led to an increased demand for skilled quantum workers and an opportunity to build a diverse workforce at the outset. In order to meet this demand and encourage women and underrepresented minorities in STEM to consider a career in QIST, we have developed a curriculum for introducing quantum computing to teachers and students at the high school level with no prerequisites. In 2022, this curriculum was delivered over the course of two one-week summer camps, one targeting teachers and another targeting students. Here, we present an overview of the objectives, curriculum, and activities, as well as results from the formal evaluation of both camps and the outlook for expanding QCaMP in future years.

physics.ed-ph↗

arXiv2022

[Dissertation] Fundamental Limits to Single-Photon Detection

Quantum mechanics cements the intimate relationship between the nature of light and its detection. Historically, quantum theories of photodetection have generally fallen into two categories: the first tries to determine what quantum field observable is measured when photoelectrons are detected, laying the theoretical groundwork for photodetection being possible. The second type are phenomenological theories, which take great care to model the details of specific photodetectors. In this dissertation, we fill in the gap between these two models in the modern literature on photodetection by constructing a fully quantum mechanical and sufficiently realistic model that includes all stages of the photodetection process: transmission, amplification, and a final classical measurement. We accomplish this within the framework of quantum information theory using the language of positive operator valued measures (POVMs). This dissertation contains material previously published in three papers: Propp, Tz. B & van Enk, S. J. (2019). On nonlinear amplification: improved quantum limits for photon counting. Optics Express 27, 16, 23454-23463. Propp, Tz. B & van Enk, S. J. (2019). Quantum networks for single photon detection. Physical Review A, 100, 033836. Propp, Tz. B & van Enk, S. J. (2020). How to project onto an arbitrary single-photon wavepacket. Physical Review A, 102, 053707.

quant-ph↗

arXiv2022

How to describe collective decay of uncoupled modes in the input-output formalism

We extend the input-output formalism to study the behavior of uncoupled discrete modes (bosonic cavity modes and fermionic qubits) when they decay to the same Markovian continuum. When the continuum interacts with only a single mode, this decay is irreversible. However, when multiple modes decay to the same Markovian continuum they develop correlations and decay collectively. In the input-output formalism these correlations manifest in additional terms in the quantum Langevin equation. For two modes this collective decay can dramatically extend the lifetimes of both modes (Dicke subradiance) and, within the single-mode subsystem, induces non-Markovian memory effects including energy back flow.

quant-ph↗

arXiv2020

How to Project onto an Arbitrary Single-Photon Wavepacket

The time-frequency degree of freedom of the electromagnetic field is the final frontier for single-photon measurements. The temporal and spectral distribution a measurement retrodicts (that is, the state it projects onto) is determined by the detector's intrinsic resonance structure. In this paper, we construct ideal and more realistic positive operator-valued measures (POVMs) that project onto arbitrary single-photon wavepackets with high efficiency and low noise. We discuss applications to super-resolved measurements and quantum communication. In doing so we will give a fully quantum description of the entire photo detection process, give prescriptions for (in principle) performing single-shot Heisenberg-limited time-frequency measurements of single photons, and discuss fundamental limits and trade-offs inherent to single-photon detection.

quant-ph↗

arXiv2019

Quantum Networks for Single Photon Detection

Single photon detection generally consists of several stages: the photon has to interact with one or more charged particles, its excitation energy will be converted into other forms of energy, and amplification to a macroscopic signal must occur, thus leading to a "click." We focus here on the part of the detection process before amplification (which we have studied in a separate publication). We discuss how networks consisting of coupled discrete quantum states and structured continua (e.g. band gaps) provide generic models for that first part of the detection process. The input to the network is a continuum (the continuum of single-photon states), the output is again a continuum describing the next irreversible step. The process of a single photon entering the network, its energy propagating through that network and finally exiting into another output continuum of modes can be described by a single dimensionless complex transmission amplitude, $T(ω)$. We discuss how to obtain from $T(ω)$ the photo detection efficiency, how to find sets of parameters that maximize this efficiency, as well as expressions for other input-independent quantities such as the frequency-dependent group delay and spectral bandwidth. We then study a variety of networks and discuss how to engineer different transmission functions $T(ω)$ amenable to photo detection.

quant-ph↗

arXiv2019

On Nonlinear Amplification: Improved Quantum Limits for Photon Counting

We show that detection of single photons is not subject to the fundamental limitations that accompany quantum linear amplification of bosonic mode amplitudes, even though a photodetector does amplify a few-photon input signal to a macroscopic output signal. Alternative limits are derived for \emph{nonlinear} photon-number amplification schemes with optimistic implications for single-photon detection. Four commutator-preserving transformations are presented: one idealized (which is optimal) and three more realistic (less than optimal). Our description makes clear that nonlinear amplification takes place, in general, at a different frequency $ω'$ than the frequency $ω$ of the input photons. This can be exploited to suppress thermal noise even further up to a fundamental limit imposed by amplification into a single bosonic mode. A practical example that fits our description very well is electron-shelving.

quant-ph↗