Quantum random number generator based on spin noise

We present an implementation of a robust quantum random number generator based on the quantum fluctuations of the collective spin of an alkali-metal vapor. The achieved bit rate is limited by the spin relaxation rate of the alkali-metal atoms $1/T_2$ to about 1 kbit/s. However, the same physical scheme, which is impervious to limitations posed by single-photon detectors used in current implementations and rests solely on threshold detection, can be extended to solid state systems with a bit rate higher than 1 Gbit/s.

Figure 1

Experimental setup. LP, linear polarizer; PBS, polarizing beam splitter; PD, photodiode; BPF, band-pass filter.

Figure 2

(a) Polarimeter signal as a function of time. Filter output noise without spins (magnetic field off) is shown in white, spin noise signal (magnetic field on) is shown in gray. The dashed lines are the positive and negative thresholds, which when exceeded, produce the random bits “1” and “0,” respectively. (b) Evolution of the ratio $N_1/N$ with the number of acquired bits. We show two different realizations of the spin noise QRNG, each consisting of ${10}^6\text{bits}$, along with one produced with the RNG of MATHEMATICA®. $N_1$ is the number of 1’s among the $N$ bits.

Figure 3

Signal to noise ratio vs probe laser power, showing the saturating behavior expected from a spin noise signal. What is plotted is the square root of Eq. (1). Inset: part of the set of spin noise spectra used for the curve.

Figure 4

(a) Occurrence of blocks of zeros (solid line) and ones (dashed line). (b) Bit autocorrelation as a function of bit distance $n$.