arXiv subjects

Abdullah Irfan

Publications and source records attributed to Abdullah Irfan.

7 recordsLinked to original sources

arXiv2025

Autonomous stabilization of remote entanglement in a cascaded quantum network

Remote entanglement between widely separated qubits is a fundamental quantum phenomenon and a critical resource for quantum information applications. Generating entanglement between independent qubits separated by arbitrary, potentially large distances requires propagating quantum states, and is typically achieved using pulsed protocols combining distinct steps of local entanglement generation followed by distribution. This necessity raises an intriguing question: Can remote entanglement be stabilized indefinitely, instead of only periodically regenerated and redistributed after decay? Here, we demonstrate that this is indeed possible, reporting autonomous stabilization of entanglement between two separate superconducting-qubit devices. Combining nonreciprocal waveguide coupling and local driving, we experimentally realize a symmetry-based coherent quantum-absorber scheme in a cascaded network. We quantify the degree of entanglement through quantum state tomography, finding that the protocol's entangling power is severely limited by imperfections that break the required symmetry. We show, however, that a modified protocol based on an alternate symmetry is far more robust, enabling us to achieve a concurrence approaching 0.5, a limit set only by local loss in the network. Our results enable on-demand delivery of high-fidelity entanglement in modular quantum processors and networks and pave the way for autonomously protecting distributed quantum information.

quant-ph↗

arXiv2024

A high-efficiency plug-and-play superconducting qubit network

Modular architectures are a promising approach to scale quantum devices to the point of fault tolerance and utility. Modularity is particularly appealing for superconducting qubits, as monolithically manufactured devices are limited in both system size and quality. Constructing complex quantum systems as networks of interchangeable modules can overcome this challenge through `Lego-like' assembly, reconfiguration, and expansion, in a spirit similar to modern classical computers. First prototypical superconducting quantum device networks have been demonstrated. Interfaces that simultaneously permit interchangeability and high-fidelity operations remain a crucial challenge, however. Here, we demonstrate a high-efficiency interconnect based on a detachable cable between superconducting qubit devices. We overcome the inevitable loss in a detachable connection through a fast pump scheme, enabling inter-module SWAP efficiencies at the 99%-level in less than 100 ns. We use this scheme to generate high-fidelity entanglement and operate a distributed logical dual-rail qubit. At the observed ~1% error rate, operations through the interconnect are at the threshold for fault-tolerance. These results introduce a modular architecture for scaling quantum processors with reconfigurable and expandable networks.

quant-ph↗

arXiv2024

Parametrically controlled chiral interface for superconducting quantum devices

Nonreciprocal microwave routing plays a crucial role for measuring quantum circuits, and allows for realizing cascaded quantum systems for generating and stabilizing entanglement between non-interacting qubits. The most commonly used tools for implementing directionality are ferrite-based circulators. These devices are versatile, but suffer from excess loss, a large footprint, and fixed directionality. For utilizing nonreciprocity in scalable quantum circuits it is desirable to develop efficient integration of low-loss and in-situ controllable directional elements. Here, we report the design and experimental realization of a minimal controllable directional interface that can be directly coupled to superconducting qubits. In the presented device, nonreciprocity is realized through a combination of interference and phase-controlled parametric pumping. We have achieved a maximum directionality of around 30\,dB, and the performance of the device is predicted quantitatively from independent calibration measurements. Using the excellent agreement of model and experiment, we predict that the circuit will be useable as a chiral qubit interface with inefficiencies at the one-percent level or below. Our work offers a promising route for realizing high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, and provides a path for isolator-free qubit readout schemes.

quant-ph↗

arXiv2024

Exact Results for a Boundary-Driven Double Spin Chain and Resource-Efficient Remote Entanglement Stabilization

We derive an exact solution for the steady state of a setup where two $XX$-coupled $N$-qubit spin chains (with possibly non-uniform couplings) are subject to boundary Rabi drives, and common boundary loss generated by a waveguide (either bidirectional or unidirectional). For a wide range of parameters, this system has a pure entangled steady state, providing a means for stabilizing remote multi-qubit entanglement without the use of squeezed light. Our solution also provides insights into a single boundary-driven dissipative $XX$ spin chain that maps to an interacting fermionic model. The non-equilibrium steady state exhibits surprising correlation effects, including an emergent pairing of hole excitations that arises from dynamically constrained hopping. Our system could be implemented in a number of experimental platforms, including circuit QED.

quant-ph↗

arXiv2024

Loss resilience of driven-dissipative remote entanglement in chiral waveguide quantum electrodynamics

Establishing limits of entanglement in open quantum systems is a problem of fundamental interest, with strong implications for applications in quantum information science. Here, we study limits of entanglement stabilization between remote qubits. We theoretically investigate the loss resilience of driven-dissipative entanglement between remote qubits coupled to a chiral waveguide. We find that by coupling a pair of storage qubits to the two driven qubits, the steady state can be tailored such that the storage qubits show a degree of entanglement that is higher than what can be achieved with only two driven qubits coupled to the waveguide. By reducing the degree of entanglement of the driven qubits, we show that the entanglement between the storage qubits becomes more resilient to waveguide loss. Our analytical and numerical results offer insights into how waveguide loss limits the degree of entanglement in this driven-dissipative system, and offers important guidance for remote entanglement stabilization in the laboratory, for example using superconducting circuits.

quant-ph↗

arXiv2023

Continuous dynamical decoupling of spin chains: Inducing two-qubit interactions to generate perfect entanglement

Efficient control over entanglement in spin chains is useful for quantum information processing applications. In this paper, we propose the use of a combination of two different configurations of strong static and oscillating fields to control and generate near-perfect entanglement between any two spins in a spin chain, even in the presence of noise. This is made possible by the fact that our control fields not only decouple the spin chain from its environment but also selectively modify the spin-spin interactions. By suitably tuning these spin-spin interactions via the control fields, we show that the quantum state of any two spins in the spin chain can be made to be a Bell state. We illustrate our results for various spin chains, such as the XY model, the XYZ model, and the Ising spin chain.

quant-ph↗

arXiv2021

Helicity-selective Raman scattering from in-plane anisotropic α-MoO$_3$

Hyperbolic crystals like α-MoO$_3$ can support large wavevectors and photon density as compared to the commonly used dielectric crystals, which makes them a highly desirable platform for compact photonic devices. The extreme anisotropy of the dielectric constant in these crystals is intricately linked with the anisotropic character of the phonons, which along with photon confinement leads to the rich physics of phonon polaritons. However, the chiral nature of phonons in these hyperbolic crystals have not been studied in detail. In this study, we report our observations of helicity selective Raman scattering from flakes of α-MoO$_3$. Both helicity-preserving and helicity-reversing Raman scattering are observed. We observe that helical selectivity is largely governed by the underlying crystal symmetry. This study shed light on the chiral character of the high symmetry phonons in these hyperbolic crystals. It paves the way for exploiting proposed schemes of coupling chiral phonon modes into propagating surface plasmon polaritons and for compact photonic circuits based on helical polarized light.

physics.optics↗