Storage and retrieval of microwave pulses with molecular spin ensembles

Abstract

Hybrid architectures combining complementary quantum systems will be largely used in quantum technologies and the integration of different components is one of the key issues. Thanks to their long coherence times and the easy manipulation with microwave pulses, electron spins hold a potential for the realization of quantum memories. Here, we test diluted oxovanadium tetraphenyl porphyrin (VO(TPP)) as a prototypical molecular spin system for the Storage/Retrieval of microwave pulses when embedded into planar superconducting microwave resonators. We first investigate the efficiency of several pulse sequences in addressing the spins. The Carr-Purcell and the Uhrig Dynamical Decoupling enhance the memory time up to three times with three π pulses. We then successfully store and retrieve trains of up to 5 small pulses by using a single recovery pulse. These results demonstrate the memory capabilities of molecular spin ensembles when embedded into quantum circuits.

Room‐Temperature Quantum Memories Based on Molecular Electron Spin Ensembles

“…With the advent of cavity QED, the idea has resurfaced in recent years, where the aim is to eventually store single photons. [ 32,33,46,51 ] In the following, we explore the possibility to store microwave pulses in inhomogeneously broadened spin ensembles in more detail. To this end, we employed a hybrid system of a 5.5 mg BDPA pellet mounted in a copper FPR tuned to ω c /2π = 35.000 GHz ( T = 7 K, Ω eff /2π = 62 MHz), with an applied field strength such that that ω s = ω c .…”

“…This is many orders of magnitude better than the storage efficiency of η = 1 × 10 −10 reported at room temperature for a system in the weak coupling regime. [ 33,68 ] An comparable efficiency of 4.5 × 10 −5 was achieved, but only at 2 K. [ 46 ] Only by decreasing the thermal energy by an order of magnitude, better storage efficiencies of η = 3 × 10 −3 are possible. [ 68,69 ] Because the collective coupling strength increases with the number of spins in the samples, microwave quantum memories based in spin ensembles have macroscopic dimensions.…”

“…Thus spin density is an important design criterion. Here magnetically dense organic radicals such as BDPA (1.5 × 10 18 mm −3 ) clearly outperform NV − centers (10 15 mm −3 [ 70 ] ), P:Si (10 14 mm −3 [ 45 ] ), and even other molecular solids such as VO(TPP):TiO(TPP) (2.3 × 10 16 mm −3 [ 46 ] ). The storage time, which is essentially given by the coherence time of the strongly coupled ensemble (Table 1) is a further important performance indicator.…”

“…[ 22 ] Self refocusing echoes were observed in inhomogeneously broadened spin systems. [ 44,45 ] Finally, microwave pulse storage and retrieval experiments were carried out in superconducting resonators at temperatures up to 2 K. [ 46 ] However, these measurements were all carried out at low to ultralow temperatures.…”

Broad-band spectroscopy of a vanadyl porphyrin: a model electronuclear spin qudit

“…This possibility has been recently used to implement single qubit operations on a related system by means of on-chip resonators. 30 In order to exploit the multiple spin states, the coupling to open transmission lines allows generating broad-band control electromagnetic pulses, at the cost of reducing the electromagnetic field amplitude. In the case of [VOTCPPEt], relevant frequencies range between a few hundred MHz up to 2 GHz at low fields.…”