Re: [time-nuts] Gentlemen: Synchronize Your Watches!

[Attila Kinali]

On Sat, 5 Nov 2016 04:19:08 + (UTC)
Perry Sandeen via time-nuts  wrote:

> Time may be relative, but physicists are a stickler for accuracy.

Ok.. the story without out the whole media mambojambo and mixup
of things can be found at [1]. A description of the setup they used
can be found at [2] and [3]. What they basically do is to use two
fs frequency combs running at 200MHz, each on the transmitter and
receiver side and implement a two-way frequency and  time transfer
using those pulses.

Attila Kinali


[1] "Synchronization of clocks through 12km of strongly turbulent air
over a city", by Sinclari et al. 2016
http://dx.doi.org/10.1063/1.4963130

[2] "Synchronization of Distant Optical Clocks at the Femtosecond Level",
by Deschenes et al. 2016
http://dx.doi.org/10.1103/PhysRevX.6.021016
https://arxiv.org/abs/1509.07888

[3] "Tight real-time synchronization of a microwave clock to an optical
clock across a turbulent air path", by Bergeron et al. 2016
http://dx.doi.org/10.1364/OPTICA.3.000441


-- 
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[time-nuts] Gentlemen: Synchronize Your Watches!

[Perry Sandeen via time-nuts]

List

Time may be relative, but physicists are a stickler for accuracy.

While many of us may give a few minutes’ grace to the timepieces in our homes, 
one group of scientists has successfully synchronized a pair of optical clocks 
to within a million billionths of a second.

By measuring time to such a fine point of accuracy, physicists could ultimately 
change the length of a second.

Scientists have managed to synchronize two optical clocks 12 km apart to within 
a quintillionth of a second. By measuring time to such a fine point of 
accuracy, physicists could ultimately change our longstanding units for how 
time is measured

World's most accurate clocks are synchronised to a quadrillionth of a second - 
and it could change how we define time

SUPER ACCURACTE CLOCKS 

Physicists in the US fired a laser beam between two buildings more than seven 
miles (12 km) apart.

At either end they used optical clocks to detect regular laser pulses every 
five nanoseconds – five billionths of a second – just like ticking of a clock.

The two clocks send the pulses to each other, with the arrival time measured at 
each clock.
The measurements were so fine that they even took the swaying of the buildings 
and air turbulence into account, to account for tiny changes which could affect 
the arrival times of the pulses.
Once the tiny differences were taken into account, the clocks could be 
synchronized to within a quadrillionth of a second.
In order to make such precise measurements, a team led by physicists at the US 
National Institutes of Standards and Technology (NIST) in Colorado fired a 
laser beam from one building to another, more than seven miles (12 km) away.
At either end they used optical clocks, which work in a similar way to 
microwave clocks, using atoms or ions which oscillate about 100,000 times 
higher than microwave frequencies, in the optical, or visible, part of the 
electromagnetic spectrum.
Using a specialized laser tool called a frequency comb, they were able to 
detect regular laser pulses every five nanoseconds – five billionths of a 
second – just like ticking of a clock.The two clocks send the pulses to each 
other, with the arrival time measured at each clock.The team’s measurements 
were so minute that they even took the swaying of the buildings and air 
turbulence into account, to account for tiny changes which could affect the 
arrival times of the pulses.
Accounting for these differences meant they could be subtracted from any 
difference in arrival times to synchronize the two to within a quadrillionth of 
a second.
Once we measure the difference of the clock times, we can speed up or slow down 
the clock at site B so that it agrees with the clock at site A to within 
femtoseconds,’ explained Laura Sinclair, a physicist at the NIST.
Writing in the journal Applied Physical Letters, the team reports the how they 
were able to maintain such a fine degree of accuracy in spite of such large 
distances.More accurately keeping would enable financial networks to use more 
precise time stamps, so handle even more transactions in shorter amounts of 
time. It would also allow GPS and other satellite-based navigation systems to 
provide even more precise location information
‘The 12 km of turbulent air results in massive distortions of the laser beams, 
yet the two clocks agree in time to 20 digits,’ said Sinclair.
The physicist added: ‘How far, in distance, can we really go?
‘If we want to someday redefine the second so that it’s based on an optical 
standard instead of a microwave standard, we’ll need to be able to link up the 
world’s best clocks and then distribute that time information.’
Earlier this year, researchers in Germany devised the method to measure 
precisely how long a second is with far more accuracy.
It could mean the definition for what a second actually is will change by an 
incomprehensibly tiny amount - just a fraction of a quadrilltionth of a second. 
 

The change will see the amount of error in estimating the length of a second 
reducing from 0.25 quadrilliionths of a second - that is 0.25 with 15 zeros in 
front of it - by a factor of ten.Reducing the amount of uncertainty in how long 
a second is means physicists will be able to make much more accurate estimates 
of how long events take.
 In context, it means such clocks would only have lost about 100 seconds since 
the universe began, 14 billion years ago.

Read more: 
http://www.dailymail.co.uk/sciencetech/article-3834518/World-s-accurate-clocks-synchronised-quadrillionth-second-change-define-time.html#ixzz4MtN7WvBJ
 

Regards,
Perrier
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