Low-noise modular microsusceptometer using nearly quantum limited dc SQUIDs

Abstract

A flexible combination of superconducting integrated circuits was used to construct a low-temperature magneto-optic microsusceptometer utilizing a dc superconducting quantum inteference device (SQUID) detector operating near the quantum limit (coupled energy sensitivity of 1.7ℏ). Miniature pick-up loop assemblies on transparent substrates were joined by superconducting interchip connections to a thin-film dc SQUID, which is in turn read out by a second dc SQUID connected to room-temperature electronics. Measurements on an 8.5-μm-diam titanium dot evaporated directly into the pick-up loop demonstrate a spin sensitivity of ∼103 spins/(Hz)1/2 at T=290 mK.

A scanning superconducting quantum interference device with single electron spin sensitivity

“…In contrast, the Pb SOTs display flux noise as low as ܵ ) ଵȀଶ = 50 nΦ 0 /Hz 1/2 . This is one of the lowest flux noise levels ever achieved [16][17][18] in SQUIDs. The ultimate flux noise in SQUIDs is determined by the quantum noise 8,19 …”

Alternating current magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a micro superconducting quantum interference device

“…This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies. The ac magnetic susceptibility of magnetic nanoparticles and single molecule magnets (SMMs) provides useful information on their spin and magnetic anisotropy, 1 as well as on the magnetic relaxation mechanisms.2-4 Miniaturized superconducting quantum interference devices [5][6][7][8][9] (SQUIDs) should eventually become capable 8,10 of measuring the magnetization reversal of a SMM (µ i ∼ 20µ B for the archetypal Mn 12 molecule). However, detecting the linear response sets even more stringent conditions: at T = 1 K, a magnetic field H = 24 A/m (0.3 Oe) induces a magnetic polarization µ ≃ 0.007µ B on the same Mn 12 cluster.…”

“…2-4 Miniaturized superconducting quantum interference devices [5][6][7][8][9] (SQUIDs) should eventually become capable 8,10 of measuring the magnetization reversal of a SMM (µ i ∼ 20µ B for the archetypal Mn 12 molecule). However, detecting the linear response sets even more stringent conditions: at T = 1 K, a magnetic field H = 24 A/m (0.3 Oe) induces a magnetic polarization µ ≃ 0.007µ B on the same Mn 12 cluster.…”

Strongly coupled, low noise dc-SQUID amplifiers

“…The properties of this SQUID amplifier are even more promising, see for example reference [16] or chapter 8 in reference [3]. The minimum sensitivity that can be reached in a measurement is predicted to be quantum limited [16][17][18] and some experiments on dc-SQUIDs or related devices approach this limit [19,20]. Possible applications of SQUID amplifiers are for example voltmeters [21], metrology [22,23], the readout of cryogenic particle detectors [24,25] or the detection of gravitational waves [26][27][28][29].…”

“…One way to solve this problem is a two-stage SQUID setup [2,18,89,90], which is shown in Fig. 1.6(b).…”