arXiv subjects

Daiqin Su

Publications and source records attributed to Daiqin Su.

At least 19 recordsLinked to original sources

arXiv2025

Mass distribution of ultralight boson in binary black hole systems

Ultralight bosons are compelling dark-matter candidates. Both scalar and vector bosons can be produced through black hole superradiance, forming a boson cloud surrounding a rotating black hole. Self-interaction of bosons, together with transition mixing in binary black hole systems, give rise to dynamical phenomena that could be potentially observable with future gravitational wave observations. In this work, we investigate the dynamics of bosons in binary black hole systems. In particular, we focus on boson mass transfer in unequal-mass binary black hole systems with arbitrary spin-orientation of the companion. Our results show that the mass ratio between the companion and the primary black holes significantly affects cloud absorption through mass transfer. Moreover, when the companion's spin is not aligned with that of the primary, the efficiency of cloud depletion is further modified.

gr-qc↗

arXiv2025

A graph-based approach to entanglement entropy of quantum error correcting codes

We develop a graph-based method to study the entanglement entropy of Calderbank-Shor-Steane quantum codes. This method offers a straightforward interpretation for the entanglement entropy of quantum error correcting codes through graph-theoretical concepts, shedding light on the origins of both the local and long-range entanglement. Furthermore, it inspires an efficient computational scheme for evaluating the entanglement entropy. We illustrate the method by calculating the von Neumann entropy of subsystems in toric codes and two types of quantum low-density-parity check codes, and by comparing the scaling behavior of the entanglement entropy with respect to the subsystem size. Our method provides a new perspective for understanding the entanglement structure in quantum many-body systems.

quant-ph↗

arXiv2025

Quantum memory based on concatenating surface codes and quantum Hamming codes

Designing quantum error correcting codes that promise a high error threshold, low resource overhead and efficient decoding algorithms is crucial to achieve large-scale fault-tolerant quantum computation. The concatenated quantum Hamming code is one of the potential candidates that allows for constant space overhead and efficient decoding. We study the concatenation of surface codes with quantum Hamming codes as a quantum memory, and estimate its error threshold, resource overhead and decoding time. A high error threshold is achieved, which can in principle be pushed up to the threshold of the surface code. Furthermore, the concatenated codes can suppress logical errors to a much lower level than the surface codes, under the assumption of comparable amount of resource overhead. The advantage in suppressing errors starts to show for a quantum memory of intermediate scale. Concatenating surface codes with quantum Hamming codes therefore provides a promising avenue to demonstrate small-scale fault-tolerant quantum circuits in the near future, and also paves a way for large-scale fault-tolerant quantum computation.

quant-ph↗

arXiv2023

Mass transfer and boson cloud depletion in a binary black hole system

Ultralight boson is one of the potential candidates for dark matter. If exists, it can be generated by a rapidly rotating black hole via superradiance, extracting the energy and angular momentum of the black hole and forming a boson cloud. The boson cloud can be affected by the presence of a companion star, generating fruitful dynamical effects and producing characteristic gravitational wave signals. We study the dynamics of the boson cloud in a binary black hole system, in particular, we develop a framework to study the mass transfer between two black holes. It is found that bosons occupying the growing modes of the central black hole can jump to the decaying modes of the companion black hole, resulting in cloud depletion. This mechanism of cloud depletion is different from that induced by the resonant perturbation from the companion.

gr-qc↗

arXiv2023

Correcting biased noise using Gottesman-Kitaev-Preskill repetition code with noisy ancilla

Concatenation of a bosonic code with a qubit code is one of the promising ways to achieve fault-tolerant quantum computation. As one of the most important bosonic codes, Gottesman-Kitaev-Preskill (GKP) code is proposed to correct small displacement error in phase space. If the noise in phase space is biased, square-lattice GKP code can be concatenated with XZZX surface code or repetition code that promises a high fault-tolerant threshold to suppress the logical error. In this work, we study the performance of GKP repetition codes with physical ancillary GKP qubits in correcting biased noise. We find that there exists a critical value of noise variance for the ancillary GKP qubit such that the logical Pauli error rate decreases when increasing the code size. Furthermore, one round of GKP error correction has to be performed before concatenating with repetition code. Our study paves the way for practical implementation of error correction by concatenating GKP code with low-level qubit codes.

quant-ph↗

arXiv2021

Universal quantum computation with optical four-component cat qubits

We propose a teleportation-based scheme to implement a universal set of quantum gates with a four-component cat code, assisted by appropriate entangled resource states and photon number resolving detection. The four-component cat code features the ability to recover from single photon loss. Here, we propose a concrete procedure to correct the single photon loss, including detecting the single photon loss event and recovering the initial states. By concatenating with standard qubit error correcting codes, we estimate the loss threshold for fault-tolerant quantum computation and obtain a significant improvement over the two-component cat code.

quant-ph↗

arXiv2021

Error mitigation on a near-term quantum photonic device

Photon loss is destructive to the performance of quantum photonic devices and therefore suppressing the effects of photon loss is paramount to photonic quantum technologies. We present two schemes to mitigate the effects of photon loss for a Gaussian Boson Sampling device, in particular, to improve the estimation of the sampling probabilities. Instead of using error correction codes which are expensive in terms of their hardware resource overhead, our schemes require only a small amount of hardware modifications or even no modification. Our loss-suppression techniques rely either on collecting additional measurement data or on classical post-processing once the measurement data is obtained. We show that with a moderate cost of classical post processing, the effects of photon loss can be significantly suppressed for a certain amount of loss. The proposed schemes are thus a key enabler for applications of near-term photonic quantum devices.

quant-ph↗

arXiv2021

Graph isomorphism and Gaussian boson sampling

We introduce a connection between a near-term quantum computing device, specifically a Gaussian boson sampler, and the graph isomorphism problem. We propose a scheme where graphs are encoded into quantum states of light, whose properties are then probed with photon-number-resolving detectors. We prove that the probabilities of different photon-detection events in this setup can be combined to give a complete set of graph invariants. Two graphs are isomorphic if and only if their detection probabilities are equivalent. We present additional ways that the measurement probabilities can be combined or coarse-grained to make experimental tests more amenable. We benchmark these methods with numerical simulations on the Titan supercomputer for several graph families: pairs of isospectral nonisomorphic graphs, isospectral regular graphs, and strongly regular graphs.

quant-ph↗

arXiv2021

Blueprint for a Scalable Photonic Fault-Tolerant Quantum Computer

Photonics is the platform of choice to build a modular, easy-to-network quantum computer operating at room temperature. However, no concrete architecture has been presented so far that exploits both the advantages of qubits encoded into states of light and the modern tools for their generation. Here we propose such a design for a scalable and fault-tolerant photonic quantum computer informed by the latest developments in theory and technology. Central to our architecture is the generation and manipulation of three-dimensional hybrid resource states comprising both bosonic qubits and squeezed vacuum states. The proposal enables exploiting state-of-the-art procedures for the non-deterministic generation of bosonic qubits combined with the strengths of continuous-variable quantum computation, namely the implementation of Clifford gates using easy-to-generate squeezed states. Moreover, the architecture is based on two-dimensional integrated photonic chips used to produce a qubit cluster state in one temporal and two spatial dimensions. By reducing the experimental challenges as compared to existing architectures and by enabling room-temperature quantum computation, our design opens the door to scalable fabrication and operation, which may allow photonics to leap-frog other platforms on the path to a quantum computer with millions of qubits.

quant-ph↗

arXiv2019

A quantum hardware-induced graph kernel based on Gaussian Boson Sampling

A device called a 'Gaussian Boson Sampler' has initially been proposed as a near-term demonstration of classically intractable quantum computation. As recently shown, it can also be used to decide whether two graphs are isomorphic. Based on these results we construct a feature map and graph similarity measure or 'graph kernel' using samples from the device. We show that the kernel performs well compared to standard graph kernels on typical benchmark datasets, and provide a theoretical motivation for this success, linking the distribution of a Gaussian Boson Sampler to the number of matchings in subgraphs. Our results contribute to a new way of thinking about kernels as a (quantum) hardware-efficient feature mapping, and lead to an interesting application for near-term quantum computing.

quant-ph↗

arXiv2019

A duality at the heart of Gaussian boson sampling

Gaussian boson sampling (GBS) is a near-term quantum computation framework that is believed to be classically intractable, but yet rich of potential applications. In this paper we study the intimate relation between distributions defined over classes of samples from a GBS device with graph matching polynomials. For this purpose, we introduce a new graph polynomial called the displaced GBS polynomial, whose coefficients are the coarse-grained photon-number probabilities of an arbitrary undirected graph $G$ encoded in a GBS device. We report a discovery of a duality between the displaced GBS polynomial of $G$ and the matching polynomial of $G\,\square\,P_2(x)$ - the Cartesian graph product of $G$ with a single weighted edge also known as the prism over $G$. Besides the surprising insight gained into Gaussian boson sampling, it opens the door for the new way of classically simulating the Gaussian boson sampling device. Furthermore, it motivates the recent success of a new type of coarse-grained quantum statistics used to construct feature maps in [Schuld et al. 2019].

quant-ph↗

arXiv2019

Hybrid spatiotemporal architectures for universal linear optics

We present two hybrid linear-optical architectures that simultaneously exploit spatial and temporal degrees of freedom of light to effect arbitrary discrete unitary transformations. Our architectures combine the benefits of spatial implementations of linear optics, namely low loss and parallel operation, with those of temporal implementations, namely modest resource requirements and access to transformations of potentially unbounded size. We arrive at our architectures by devising and employing decompositions of large discrete unitary transformations into smaller ones, decompositions we expect to have broad utility beyond spatio-temporal linear optics. We show that hybrid architectures promise important advantages over both spatial-only and temporal-only architectures.

quant-ph↗

arXiv2019

Generation of photonic non-Gaussian states by measuring multimode Gaussian states

We present a detailed analytic framework for studying multimode non-Gaussian states that are conditionally generated when few modes of a multimode Gaussian state are subject to photon-number-resolving detectors. From the output state Wigner function, we deduce that the state factorizes into a Gaussian gate applied to a finite Fock-superposition non-Gaussian state. The framework provides an approach to find the optimal strategy to generate a given target non-Gaussian state. We explore examples, such as the generation of cat states, weak cubic phase states, and bosonic code states, and achieve improvements of success probability over other schemes. Our framework also applies to the case in which the measured Gaussian state is mixed which is very important for the analysis of experimental imperfections such as photon loss. The framework has potential far-reaching implications to the generation of bosonic error-correcting codes and for the implementation of non-Gaussian gates using resource states, among other applications requiring non-Gaussianity

quant-ph↗

arXiv2019

Conversion of Gaussian states to non-Gaussian states using photon-number-resolving detectors

Generation of high fidelity photonic non-Gaussian states is a crucial ingredient for universal quantum computation using continous-variable platforms, yet it remains a challenge to do so efficiently. We present a general framework for a probabilistic production of multimode non-Gaussian states by measuring few modes of multimode Gaussian states via photon-number-resolving detectors. We use Gaussian elements consisting of squeezed displaced vacuum states and interferometers, the only non-Gaussian elements consisting of photon-number-resolving detectors. We derive analytic expressions for the output Wigner function, and the probability of generating the states in terms of the mean and the covariance matrix of the Gaussian state and the photon detection pattern. We find that the output states can be written as a Fock basis superposition state followed by a Gaussian gate, and we derive explicit expressions for these parameters. These analytic expressions show exactly what non-Gaussian states can be generated by this probabilistic scheme. Further, it provides a method to search for the Gaussian circuit and measurement pattern that produces a target non-Gaussian state with optimal fidelity and success probability. We present specific examples such as the generation of cat states, ON states, Gottesman-Kitaev-Preskill states, NOON states and bosonic code states. The proposed framework has potential far-reaching implications for the generation of bosonic error-correction codes that require non-Gaussian states, resource states for the implementation of non-Gaussian gates needed for universal quantum computation, among other applications requiring non-Gaussianity. The tools developed here could also prove useful for the quantum resource theory of non-Gaussianity.

quant-ph↗

arXiv2018

Linear multiport photonic interferometers: loss analysis of temporally-encoded architectures

Implementing spatially-encoded universal linear multiport interferometers on integrated photonic platforms with high controllability becomes increasingly difficult as the number of modes increases. In this work, we consider an architecture in which temporally-encoded modes are injected into a chain of reconfigurable beamsplitters and delay loops, and provide a detailed loss analysis for this and other comparable architectures. This analysis also yields a straightforward and explicit description of the control sequence needed for implementing an arbitrary temporally-encoded transformation. We consider possible physical implementations of these architectures and compare their performance. We conclude that implementing a chain of reconfigurable beamsplitters and delay loops on an integrated lithum niobate platform could outperform comparable architectures in the near future.

quant-ph↗

arXiv2018

Particle production and apparent decoherence due to an accelerated time-delay

We study the radiation produced by an accelerated time-delay acting on the left moving modes. Through analysis via the Schrodinger picture, we find that the final state is a two-mode squeezed state of the left moving Unruh modes, implying particle production. We analyse the system from an operational point of view via the use of self-homodyne detection with broad-band inertial detectors. We obtain semi-analytical solutions that show that the radiation appears decohered when such an inertial observer analyses the information of the radiation from the accelerated time-delay source. We make connection with the case of the accelerated mirror. We investigate the operational conditions under which the signal observed by the inertial observer can be purified.

quant-ph↗

arXiv2018

Implementing quantum algorithms on temporal photonic cluster states

Implementing quantum algorithms is essential for quantum computation. We study the implementation of three quantum algorithms by performing homodyne measurements on a two-dimensional temporal continuous-variable cluster state. We first review the generation of temporal cluster states and the implementation of gates using the measurement-based model. Alongside this we discuss methods to introduce non-Gaussianity into the cluster states. The first algorithm we consider is Gaussian Boson Sampling in which only Gaussian unitaries need to be implemented. Taking into account the fact that input states are also Gaussian, the errors due to the effect of finite squeezing can be corrected, provided a moderate amount of online squeezing is available. This helps to construct a large Gaussian Boson Sampling machine. The second algorithm is the continuous-variable Instantaneous Quantum Polynomial circuit in which one needs to implement non-Gaussian gates, such as the cubic phase gate. We discuss several methods of implementing the cubic phase gate and fit them into the temporal cluster state architecture. The third algorithm is the continuous-variable version of Grover's search algorithm, the main challenge of which is the implementation of the inversion operator. We propose a method to implement the inversion operator by injecting a resource state into a teleportation circuit. The resource state is simulated using the Strawberry Fields quantum software package.

quant-ph↗

arXiv2018

Correcting finite squeezing errors in continuous-variable cluster states

We introduce an efficient scheme to correct errors due to the finite squeezing effects in continuous-variable cluster states. Specifically, we consider the typical situation where the class of algorithms consists of input states that are known. By using the knowledge of the input states, we can diagnose exactly what errors have occurred and correct them in the context of temporal continuous-variable cluster states. We illustrate the error correction scheme for single-mode and two-mode unitaries implemented by spatial continuous-variable cluster states. We show that there is no resource advantage to error correcting multimode unitaries implemented by spatial cluster states. However, the generalization to multimode unitaries implemented by temporal continuous-variable cluster states shows significant practical advantages since it costs only a finite number of optical elements (squeezer, beam splitter, etc).

quant-ph↗