Fabrication of superconductive optical flux trap memory cell

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Abstract

We fabricate an optical flux trap memory cell and demonstrate femtosecond (fs) optical signal detection. A memory loop to store magnetic flux quanta generated by fs optical pulses is combined with a dc-SQUID readout circuit. The results suggest that the SQUID readout can detect the flux generated in the memory loop by fs pulses.

Introduction

Previously, we reported that optical magnetic flux can be generated in a superconductive loop by femtosecond (fs) laser pulses [1]. Superconducting electrooptic applications such as flux trap memory thus can be expected [2]. In this work, we fabricate an optical flux trap memory cell and demonstrate the fs optical signal detection. The memory loop to store magnetic flux quanta is combined with a dc-SQUID readout circuit.

Section snippets

Experimental

The fs pulses with a pulse width of about 50 fs, center wavelength of about 800 nm, and repetition rate of 82 MHz are produced by a mode-locked Ti:sapphire laser. Fig. 1 shows the photograph of the fabricated memory cell. The memory loop is inductively coupled to the SQUID. The YBCO thin films grow on bicrystal MgO substrate with an angle of 24° are patterned into the structure by conventional photolithography and ion milling process. The magnetic flux created in the loop is detected by

Results and discussion

Fig. 2(b) shows the two-dimensional images of the THz radiation amplitude after flux-generation in the loop with a laser power of 30 m and a bias current of 100 mA. We see that the supercurrent distribution is clearly visualized by the present technique. The clockwise and counterclockwise supercurrent circulates in the upper and lower loops. Since we can evaluate the supercurrent density quantitatively, by assuming a loop inductance of 140 pH, the number of flux quanta φ/φ0 is estimated to be

Summary

We controlled the magnetic flux quanta in the loop and evaluated by THz radiation imaging. We also fabricated the optical flux trap memory cell.

Acknowledgments

This work was partially supported by a Grant-in-Aid for Scientific Research on Priority Area (A) under grant no.10142101 and a Grant-in-Aid for Scientific Research (B) under grant no.12450146, from the Ministry of Education, Science, Sports, and Culture, Japan.

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