arXiv subjects

Pablo J. Alonso

Publications and source records attributed to Pablo J. Alonso.

3 recordsLinked to original sources

arXiv2025

Waveguide quantum electrodynamics at the onset of spin-spin correlations

We explore the competition between light-mediated and intrinsic matter-matter interactions in waveguide quantum electrodynamics. For this, we couple a superconducting transmission line to a model magnetic material, made of organic free radical molecules with a spin $S=1/2$ and a $g_{S}$ factor very close to that of a free electron. The microwave transmission has been measured in a wide range of temperatures ($0.013$ K $\leq T \leq 2$ K), magnetic fields ($0\leq B \leq 0.5$ T) and frequencies ($0 \leq ω/2 π\leq 14$ GHz). We find that molecules belonging to one of the two crystal sublattices form one-dimensional spin chains. Temperature then controls the intrinsic correlations along these chains in a continuous and monotonic way. In the paramagnetic region ($T > 0.7$ K), the microwave transmission shows evidences for the collective coupling of quasi-identical spins to the propagating photons, with coupling strengths that reach values close to the dissipation rates. As $T$ decreases, the growth of spin correlations, combined with the anisotropy in the spin-spin exchange constants, tend to suppress the collective spin-photon coupling. In this regime, the spin visibility in transmission reflects also a gradual change in the nature of the dominant spin excitations, from single spin flips to bosonic magnons.

quant-ph↗

arXiv2020

A dissymmetric [Gd$_{2}$] coordination molecular dimer hosting six addressable spin qubits

Artificial magnetic molecules are suitable hosts to one or several spin qubits, which could then implement small-scale algorithms. In order to become of practical use, such molecular spin processors need to increase the dimension $d$ of the available computational space and fulfill the highly demanding conditions that warrant universal operations. Here, we design, synthesize and fully characterize dissymetric molecular dimers hosting either one or two Gd(III) ions. The strong sensitivity of Gd(III) magnetic anisotropy to the symmetry of its local coordination gives rise to different zero-field splittings at each coordination site. As a result, the [LaGd] and [GdLu] complexes provide realizations of distinct $d = 8$ spin qudits, whereas the [Gd$_{2}$] dimer meets all requirements, including a complete set of operations, to act as a $d = 64$ all-electron spin qudit (or, equivalenty, as six addressable qubits). Electron paramagnetic resonance experiments show that the relevant resonant transitions between different spin states can be coherently controlled, with coherence times T$_{M}$ of the order of $1$ $μ$s limited by intramolecular hyperfine interactions. Coordination complexes with embedded quantum functionalities are promising building blocks for quantum computation and simulation hybrid platforms.

quant-ph↗

arXiv2016

Three addressable spin qubits in a molecular single-ion magnet

We show that several qubits can be integrated in a single magnetic ion, using its internal electronic spin states with energies tuned by a suitably chosen molecular environment. This approach is illustrated with a nearly-isotropic Gd(III) ion entrapped in a polyoxometalate molecule. Experiments with microwave technologies, either three dimensional cavities or quantum superconducting circuits, show that this magnetic molecule possesses the number of spin states and the set of coherently addressable transitions connecting these states that are needed to perform a universal three-qubit processor or, equivalently, a d=8-level 'qudit'. Our findings open prospects for developing more sophisticated magnetic molecules which can result in more powerful and noise resilient quantum computation schemes.

cond-mat.mtrl-sci↗