Superconducting electronics are one of the best understood and most promising platforms for realising quantum information processing. Unfortunately they suffer from the presence of defects and imperfections. These include uncontrolled two-level systems, which reside in the materials used to construct them. These defects can lead to loss of energy, coherence, device aging and imperfect control...
Photon loss is the dominant source of noise in optical quantum systems. The Gottesman-Kitaev-Preskill (GKP) bosonic code provides significant protection; however, even low levels of loss can generate uncorrectable errors that another concatenated code must handle. In this work, we characterize these errors by deriving analytic expressions for the logical channel that arises from pure loss...
Cloud-based quantum computing is transforming how sensitive algorithms are executed, enabling remote access to shared hardwareโbut also introducing new risks of device impersonation and unauthorized access. We present a hardware-intrinsic authentication scheme based on Quantum Physical Unclonable Functions (Q-PUFs), which exploit fabrication-induced variations in quantum devices to create...
Quantum computers promise better scaling for problems that are intractable on classical computers, however current devices are limited by noise, which only permits shallow depth circuits and restricts the potential algorithms that can be run. Nonetheless, many error mitigation schemes have been developed which use extra quantum or classical resources to recover corrected observables from noisy...
Classical simulations of noisy quantum circuits is instrumental to our understanding of the behavior of real world quantum systems and the identification of regimes where one expects quantum advantage. The presence of noise can decay quantum entanglement. Our work capitalizes on this idea. We employ new methods that push the boundaries of noise-induced entanglement decay, using it to...
Simulating chaotic systems is difficult, due to randomness from divergent sensitivity to system parameters, and the same holds for quantum chaosโoften understood as dynamics in quantum systems that exhibit classical chaos in a large-system limit. Yet in quantum technologies, quantum chaos also arises in systems which do not possess any straightforward classical limit. For example, quantum...
Quantum technology is expected to have revolutionary impact on different areas including computation, communication, and sensing. The first step in any quantum application is state preparation, where it is required to transfer the system from a fixed initial state to a final target state. This task can be challenging to perform, especially in non-Markovian open quantum systems. Invariant-based...
Optical Very Long Baseline Interferometry offers the potential for unprecedented angular resolution in both astronomical imaging and precision measurements. Classical approaches, however, face significant limitations due to photon loss, background noise, and the requirements for dynamical delay lines over large distances.
We surveys recent developments in quantum-enabled VLBI, which aim to...
For more than half a century, the standard quantum limit (SQL) was thought to limit the laser coherence $\mathfrak{C}$ โโ the number of photons emitted from the laser into the beam in one coherence time โโ to a scaling $\Theta(\mu^2)$, where $\mu$ is the mean number of optical-frequency excitations stored inside the laser. However, recently it has been shown [Baker et al., Nat. Phys. 17, 179...
We calculate the exact spectral function of a single impurity repulsively interacting with a bath of fermions in one-dimensional lattices, by deriving the explicit expression of the form factor for both regular Bethe states and the irregular spin-flip state and ฮท-pairing state, based on the exactly solvable one dimensional Hubbard model. While at low impurity momentum Q โผ 0 the spectral...
A typical surface-enhanced Raman scattering (SERS) system relies on deeply subwavelength field localization in nanoscale plasmonic cavities to enhance both the excitation and emission of Raman-active molecules [1,2]. Here, we demonstrate that a germanium-vacancy (GeV) defect in diamond can efficiently mediate the excitation process, by acting as a bright atomic antenna [3]. At low...
Leading designs for quantum networks require efficient microwave-to-optical signal transduction. One promising platform uses ensembles of atoms (Er3+) coupled to dual microwave-optical cavities [1]. It is projected that these devices can reach practical efficiencies by boosting the coupling between cavities and optical and microwave transitions in atoms. However, increasing these couplings...
The pursuit of highly coherent light sources is fundamental to advancements in quantum metrology, sensing, and communication. Although the Schawlow-Townes limit, where coherence scales as the square of the number of photons in the laser cavity, has long defined the standard for laser coherence, recent work [1] established a more fundamental limit, the "Heisenberg limit", where coherence scales...
Optical quantum memories are an essential optical technology with applications in quantum communications and networking, quantum sensing and optical quantum computing. Ensemble optical memories rely on a controllable, coherent interaction between light and a long-lived electronic state, with the light absorbed into and regenerated from a collective excitation of the ensemble of emitters....
Matter wave-based sensors have demonstrated exquisite sensitivity and precision, for example, for acceleration and rotation measurements that utilize interferometry. This work takes a new look at matter waves, in particular those associated with alternating currents (AC) of interacting identical neutral particles such as rubidium atoms. The semi-classical mechanics of such waves are...
All current quantum devices suffer from noise originating from system-environment interactions. Often the noise is non-Markovian, i.e. correlated across the time-steps of a quantum circuitโas reported in spin silicon platforms and the superconducting devices of IBM and Google. However, most characterisation techniques assume Markovian (uncorrelated) noise, which results in inaccurate gate...
Precise and robust control of sequences of quantum operations is essential for quantum information processing. The present quantum hardware is plagued with correlated noise, i.e., non-Markovian noise. The existing mitigation strategies, which are based on Markovian assumption, are ineffective. Multi-time process tomography aims to provide a complete description of the nature and strength of...
Quantum sensing leverages quantum resources to achieve measurement capabilities beyond what is possible classically [1,2]. While there is great focus on precision parameter estimation, an underexplored application is single-shot binary-decision making, where the task is to decide whether a signal has been detected. This is particularly advantageous when the underlying event is rare. Quantum...
Digital quantum simulation (DQS) is a promising application of quantum computers. Typically, short Trotter step sizes are required to realise accurate DQS. In the context of Trotterised DQS, it is also useful to be able to tune interaction times and even implement โnegative-timeโ gates, when implementing higher-order digitisation algorithms and to control the amount of digitisation error,...
Quantum hardware processing power is normally optimised by minimising decoherence effects from unwanted interactions with noisy environments. Yet paradoxically, carefully tailored bath interactions can be exploited to preserve coherence rather than degrade it. Engineered dissipation, or reservoir engineering, introduces tailored couplings between a quantum system and its environment to serve...
The Unruh effect, resulting from the entanglement of modes across the right and left wedges of Rindler spacetime, predicts that a uniformly accelerating observer perceives the Minkowski vacuum as a thermal bath. Despite its theoretical significance, this effect remains undetected. The Unruh effect has a timelike counterpart due to the entanglement between past and future Rindler light cones....
Higher-dimensional quantum systems (qudits) offer advantages in information encoding, error resilience, and compact gate implementations, and naturally arise in platforms such as superconducting and solid-state systems. However, realistic conditions such as non-Markovian noise, non-ideal pulses, and beyond rotating wave approximation (RWA) dynamics pose significant challenges for controlling...
High-dimensional qudit systems yield the exciting prospect of hosting error-correctable logical qubits [1]. The antimony (123Sb) donor in silicon is ideal for this purpose, because its spin-7/2 nucleus embeds an 8-dimensional Hilbert space (or 16-dimensional, including the electron [2]) that can encode Schrรถdinger cat states [3].
Scaling up this donor nuclear qubits requires using electrons...
Quantum technologies are rapidly emerging as powerful tools for addressing complex challenges in biology. In this talk, I will share a cross-section of Infleqtionโs research at the intersection of both quantum computing and quantum sensing with applications in biomedicine. On the computing side, I will describe our ongoing work within the Wellcome Leap Q4Bio program, where we have developed a...
Sensing and detection in the mid-infrared (MIR) range are crucial, as many molecules exhibit characteristic absorption bands [1]. However, traditional techniques like Fourier Transform Infrared (FTIR) spectroscopy rely on costly lasers, complex and noisy detectors often requiring cryogenic cooling, all of which limit their applicability [2]. To address these limitations, we propose a quantum...
Microscopy is central to biological discovery, but high performance often requires high illumination powers that induce photodamage. Quantum correlations offer a way to overcome this limit by enhancing the signal-to-noise ratio at fixed optical intensities.
We present a quantum microscope based on stimulated Raman scattering (SRS), a widely used technique for molecular fingerprinting...
Over the past two decades, the field of cavity optomechanics has succeeded in cooling resonant mechanical oscillators down to their quantum ground state. The success of cavity optomechanics has led to various proposals which aim to harness the quantum properties of cooled mechanical systems, including in tests of fundamental physics [1], quantum state preparation [2] and quantum metrology [3]....
Trapped-ion platforms have emerged as a powerful architecture for quantum simulation, offering high-fidelity universal control over both internal atomic states (spins) and bosonic motional modes. This makes them particularly well-suited for simulating molecular dynamics, where a natural analogy allows a moleculeโs electronic configuration to be mapped onto the ion's spin, and its vibrational...
Despite significant advances in molecular biology and microscopy techniques, many questions remain regarding the interactions between a single cell and its environment. In particular, understanding protein-membrane binding is vital for optimising the delivery of vaccines and medicines. By studying these transmembrane behaviours, we can improve drug delivery and increase the specificity of cell...
Gaussian Boson Samplers (GBS) are non-universal optical quantum computers introduced to demonstrate quantum advantage without requiring full error-correction by efficiently sampling from a classically-hard distribution. These devices are relatively simple: just squeezed states fed through a random, precise array of linear optics. Recently, the first large-scale GBS devices were created: the...
In the not-too-distant past, reliable transfer of data was largely done with small portable memories. This method is ideal for quantum communication in which the required resource for protocols such as quantum key distribution and quantum teleportation is distributed Bell pairs, as these can be distributed ahead of time using quantum memories [1410.3224].
Quantum low-density parity-check...
Exciton-polaritons (polaritons), hybrid quasiparticles formed by excitons coupled to microcavity photons, are known to undergo BoseโEinstein condensation at elevated temperatures. One of the defining features of polariton condensation is the formation of long-range order both in space and time, as demonstrated in continuous wave measurements, which is non-trivial due to the inherently...
Levitated optomechanics, the trapping and control of microscopic and mesoscopic particles in vacuum, has seen recent and widespread success including record torque sensitivity [1], and yoctonewton force sensing [2]. A levitated nanoparticle is ideal for a โmacroscopicโ quantum platform due to its intrinsic mass and low coupling to the environment. This presents an exciting avenue for...
Coherently manipulated large ion crystals in a Penning trap are a promising candidate for near-term quantum simulation of complex many-body phenomena [1]. At the University of Sydney, we have developed a Penning trap to perform such experiments with crystals containing hundreds of beryllium ions [2]. The system has recently demonstrated efficient site-resolved imaging, enabling single-shot...
QFT models involving detectors are usually modelled perturbatively out of necessity, however, there are certain situations when non-perturbative methods can be used. When the detector is a finite dimensional qudit, non-perturbative modelling is possible if the detector interacts suddenly and very quickly (ฮด-switching) or if the detector is degenerate (zero energy gap). When the detector...
The rare-earth nitrides are a series of ferromagnetic semiconductors with suitable properties for cryogenic memory applications, including quantum and superconducting computing systems. When grown as thin films, the magnetic and transport properties of rare-earth nitrides can be tuned independently by varying the growth conditions and rare-earth nitride selection [1]. In particular, solid...
Ground-state energy estimation of chemical systems is perhaps one of the most promising applications of emerging quantum processors. However, the presence of noise makes near-term implementation of quantum algorithms challenging, while fault-tolerance at the scale required for useful computation remains a medium-term prospect. We present Hamiltonian moments-based approaches to ground-state...
Estimating the ground state energy of a physical system is an important task in quantum algorithms. If the ground state can be prepared on a quantum computer, then its energy can be estimated using the quantum phase estimation algorithm, which involves applying multiples of a unitary to the ground state, controlled on an auxiliary state prepared on a control register. Textbook descriptions of...
The development of linear optical quantum computers (QCs) has accelerated in recent years, in part, due to experimental implementations of large-scale Gaussian boson sampling (GBS) devices. These QCs send squeezed state photons into a linear photonic network and output a series of photon count patterns. This seemingly simple task is #P-hard because, for implementations utilizing photon-number...
Open quantum systems evolving under time-dependent Lindbladian simulations dynamics arise in diverse contexts, yet efficient algorithms for large-scale, time-dependent Lindbladian dynamics remain underexplored. In the fault-tolerant setting, the time required to propagate a state by a complex, time-dependent Hamiltonian is prohibitive. We circumvent this issue by introducing a...
Through left- or right-handed twisting, we investigate the impact of mirror-asymmetry (chirality) of the conducting boundary conditions of an equilaterial triangular cross section electromagnetic resonator. We observe the generation of eigenmodes with nonzero electromagnetic helicity as a result of the coupling of near degenerate $\mathrm{TE}_{11(p+1)}$ and $\mathrm{TM}_{11 p}$ modes. This can...
Secure Position, Navigation and Timing (PNT) is of critical importance in modern day to day life and the contemporary state-of-the-art radio frequency-based systems are vulnerable to various intercept and signal jamming attacks. Thus, the need for development of more secure alternative PNT capabilities. Quantum entanglement provides an elegant way of sharing tightly correlated time...
Discrete Wigner functions (DWFs) are central tools for visualising states, signifying nonclassicality, and supporting quantitative analysis in quantum information, yet many inequivalent constructions coexist for each Hilbert-space dimension. This fragmentation obscures which features are fundamental and which are artefacts of representation, and it impedes quantitative comparison of...
In quantum algorithms for simulation of quantum systems, a leading method is to use a product formula approach. The Hamiltonian is written as $H=T+V$, where the kinetic energy $T$ and potential energy $V$ are each calculated. Whereas $T$ can be calculated with complexity $n$ for a system with $n$ charges, calculating $V$ has complexity $n^2$ and is therefore a bottleneck. This complexity is...
We demonstrate an optimal quantum control strategy for the deterministic preparation of entangled harmonic oscillator states in trapped ions. The protocol employs dynamical phase modulation of laser-driven Jaynes-Cummings and anti-Jaynes-Cummings interactions. We prepare Two-Mode Squeezed Vacuum (TMSV) states in the mechanical motions of a trapped ion and characterize the states with...
When a conservative superfluid flows about an impenetrable cylindrical obstacle, vortex pairs will arise at the lateral edges of the obstacle and be shed into the background fluid flow when the critical velocity is exceeded. This phenomenon was characterised using the Gross-Pitaevskii equation in a theoretical study by Frisch et al. in 1992 [1]. In 2021 Stockdale et al. [2] looked at vortex...
Converting disordered energy (heat) into ordered energy (work) is a fundamental objective in thermodynamics. In classical systems, disorder reflects practical limits on the knowledge of the microscopic state of a large system. Quantum systems, however, introduce an additional uncertainty arising from the fundamental structure of quantum mechanics [1]. Features such as coherence and...
Quantum measurements, alongside quantum states and processes, form a cornerstone of quantum information processing. The precise characterisation of this triadโof states, processes, and measurementsโunderpins how well quantum devices used across computation, communication, and sensing platforms can be calibrated, benchmarked, and ultimately trusted. However, while state and process...
