LONDON, April 5 (Xinhua) -- Scientists have for the first time measured electrons tunneling their way out of atoms at an amazing speed of less than a billionth of a millionth of a second, according to the latest issue of Nature published here Thursday.

    Electrons have a negative charge and are glued into atoms by the attractive force of its positively charged nucleus. In classical physics, an electron could not escape from an atom unless it received enough energy to overcome this force by ascending the nucleus's potential barrier.

    But quantum mechanics allows another way -- the electron can "tunnel" straight through the barrier with a certain probability. Quantum tunneling is commonplace in the microscopic world. But until now, it has proved impossible to time the process because it happens much faster than any clock could possibly measure.

    Now, German scientists have achieved the feat by giving electrons in a cloud of neon atoms three fleeting time "windows" in which they could burrow out, then counted how many took up the offer of escape, the science journal said.

    The scientists, led by Ferenc Krausz at Max Planck Institute for Quantum Optics, zapped a cloud of the neon atoms with two carefully synchronized brief laser pulses -- an ultraviolet one (pulse 1) and an infrared one (pulse 2).

    Pulse 1 primed tightly bound electrons for escape from neon atoms by raising their energy levels, so they could escape as far as the periphery of the atom. Then, three peaks of the oscillating pulse 2 provided a strong enough electric field to suppress the potential barrier from the nucleus, giving the pre-prepped electrons three windows of opportunity to escape.

    By blasting pulse 1 at different times during the course of pulse 2, then measuring the numbers of electrons liberated, the scientists could reconstruct their escape strategy.

    Around 30 percent, 40 percent and 30 percent of the electrons emerged in the three main bursts, in line with a quantum tunneling theory dating back to the 1960s.

    The results proved that a single electron could escape during a half-wave of the infrared laser, fleeing in less than 400 attoseconds - an unimaginably short time. If time was slowed down so that an attosecond lasted for 1 second, that second would last for 30 billion years -- more than twice the age of the universe.

    "This measurement is a very important step towards the goal of really understanding how tunneling happens," according to Krausz who added that a better understanding of tunneling could contribute to the development of compact X-ray lasers, in which electron tunneling looks set to play a key role.

    Current powerful X-ray lasers are cumbersome machines. Compact ones could be used in hospitals to reveal tumors when they're very small and readily treatable.

    Krausz said one of their dreams is to be able to build very compact X-ray lasers which would allow cancer diagnosis at a very early stage.