
Yale physicists find signs of a time crystal - anigbrowl
https://news.yale.edu/2018/05/02/yale-physicists-find-signs-time-crystal
======
correlator
Glad to see Sean make such a noteworthy discovery. I worked in the lab next
door and remember him being the happiest and kindest person in the building.
Kudos!

~~~
matthewwiese
The "small world" effect of HN never ceases to astound me. It's always so cool
to have somebody chime in with an anecdote about (what appears to an outsider
as) something totally niche and out-there.

~~~
DEFCON28
Sean was just Ok.

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jdrov
First author here -- happy to take any questions!

~~~
jdrov
There are a few questions about an "overview," so I'll give that a shot here.
This is some imagery I've been using recently, about how our observed
signatures are related to crystals.

Sometimes physicists think of phase transitions in terms of "symmetry
breaking." Imagine zooming in very close on the molecules in a glass of liquid
water, all tumbling quickly into and out of your field of view. The situation
is highly "symmetric": if you closed your eyes and I shifted the field of view
slightly to the left, you wouldn't know what I'd done when you opened your
eyes again.

Now suppose the water freezes into a crystal of ice, so that the molecules are
arranged on a regular lattice. If I repeat my "shift-slightly-to-the-left"
experiment, you'd be able to tell I moved things. That is, somehow the
molecules chose a particular location for the lattice, even though any other
location of the lattice could have done just as well. In jargon, we say the
water "spontaneously broke the continuous translational symmetry": the
defining _equations of motion_ are agnostic about the particular location in
space, but the _state of the system_ chose a location anyways.

In our experiment, we do something similar in time rather than space. We drive
the system with pulses once every time period "T", so the _equations of
motion_ are identical under this "discrete" shift in time. However, the _state
of the system_ (in our case, the direction of the nuclear magnetization) only
goes back to itself every time 2T, and so "breaks discrete time translational
symmetry."

There is one more important feature of the observed signature in this analogy:
if you nudge an atom that is in a crystal lattice, it will want to return to
its original position. Similarly, the period of the magnetization's direction-
reversal is robust to our pulse imperfections, if we allow the quantum
interactions long enough to act. So, the "region" of parameter space where you
can observe this effect is not confined to perfectly ideal pulses, but is
instead robust to our pulse imperfections -- the "robustness" depends on the
amount of time we allow the nuclear spin interactions to take place.

\---

I hope this helps. I recommend the synopses available at prl.aps.org, and
searching for the PDF preprints on the Arxiv (not yet quite as good as the
published versions), if you don't have Physical Review access.

\---

[Edit for links]

[2012 overview]
[https://physics.aps.org/articles/v5/116](https://physics.aps.org/articles/v5/116)

[2013 overview]
[https://physics.aps.org/articles/v6/31](https://physics.aps.org/articles/v6/31)

[2013 quanta mag.] [https://www.quantamagazine.org/perpetual-motion-test-
could-a...](https://www.quantamagazine.org/perpetual-motion-test-could-amend-
theory-of-time-20130425/)

[2017 overviews: "recipe" and first two results]

[https://physics.aps.org/articles/v10/5](https://physics.aps.org/articles/v10/5)

[https://www.nature.com/news/the-quest-to-crystallize-
time-1....](https://www.nature.com/news/the-quest-to-crystallize-time-1.21595)

[2018 announcement] [https://physics.aps.org/synopsis-
for/10.1103/PhysRevLett.120...](https://physics.aps.org/synopsis-
for/10.1103/PhysRevLett.120.180603)

[A different background by (the great) Natalie Wolchover of Quanta Mag., which
provides context for the original thrust of one branch of this research. Our
first significant involvement was after a talk about "Time Translational
Symmetry Breaking" by Chetan Nayak of Microsoft's Station Q.]

[https://www.quantamagazine.org/physicists-aim-to-classify-
al...](https://www.quantamagazine.org/physicists-aim-to-classify-all-possible-
phases-of-matter-20180103/)

~~~
brandmeyer
Is there any relationship between this kind of lossless vibration, and other
lossless processes like superconductivity or superfluidity?

~~~
jdrov
I'm not confident that what we're observing are "lossless vibrations," but it
is the case that there is something that is "lossless" about what we call
"unitary evolution." The signal we start with decays to zero after a while,
but we are able to show that this signal can be (in large part) restored,
demonstrating that much of what initially looked like irretrievable loss is
actually what we think of as "evolution towards a complicated but coherent
state."

~~~
brandmeyer
I'm more confused, now. Some of the articles you linked to talk about time
crystals as a type of perpetual motion machine, albeit one that is "exactly
unity" instead of "over unity" as the crackpots would say.

If you have to hit the system with an impulse every once in a while to keep it
toggling, how is it different than any other kind of resonant oscillating
system? Is it that the cycle goes through states like:

* disorganized

* organized, directional

* disorganized

* organized, opposite direction

I still feel like the part of this system that is special and interesting is
getting lost in the translation to lay language :(

~~~
jdrov
This is a good question. The "directions" you mention would, in our system,
typically be considered to depend on the nature of the drive. For instance, if
you repeatedly rotate the magnetization by 180 degrees, you can imagine the
magnetization going up-down-up-down-... repeatedly, whereas if you instead
used rotations of 181 degrees, it would take a long time for the state to come
back around to pointing along its exact original orientation.

The proposed signature of a "discrete time crystal" was to observe the
magnetization point up-down-up-down-... even when you used e.g. 181 degree
rotations, _if_ you allow dipole-dipole interactions to act for long enough
between rotations. This is what we observe: "wrapped" magnetization when we
use imperfect rotations with short nuclear spin interaction times, then locked
up-down-up-down-... magnetization when we use imperfect rotations with longer
nuclear spin interaction times.

A last subtelty when comparing to traditional oscillating systems is that the
response is not at the same frequency as the drive, but will have a period
determined by both the drive period T and the symmetry of the dipole
interactions. Our system's interactions have 2 symmetric states, so the
response period is at 2T. Other systems have other symmetries; for instance,
the research team at Harvard showed oscillations at 3T using a spin system
with different interaction symmetries.

~~~
brandmeyer
(HN doesn't do private messages, or this would be sent privately)

Thanks for coming out here and fielding our totally ignorant questions. Its an
amazing and beautiful world out there, thank you for sharing your discoveries
about it.

~~~
jdrov
Thanks for the kind words. I've focused a good deal in the past few years on
teaching/communication (see my profile for a link to some of my basic-physics
lectures for student taking the MCAT), and I'm very grateful for the
opportunity to discuss our work with this community. Thanks for your interest
and great questions!

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perlgeek
> a time crystal — a form of matter that “ticks” when exposed to an
> electromagnetic pulse

what a fancy name.

We would have called that an "oscillator" or a "resonator" or so back in the
days :)

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h0rse
Out of curiosity, how is this different from the crystals used for timing in a
small electronic device like an arduino? Is this an effect different from the
piezoelectric effect?

~~~
gcb0
instead of readily usable voltage/current changes, you get (so far) useless,
probably cased by the measurements, electron spin in one direction or another
flipping over time.

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freeflight
Most of this stuff goes way above my head, but I remember that creating time
crystals used to be a thing last year? [0]

What's so special about these Yale time crystals, are they of a different type
then these previous ones? This all feels a bit weird like there's some kind of
secretive time crystal production going on, by people initiated into the dark
arts of metaphysics.

[0]
[https://news.ycombinator.com/item?id=13505287](https://news.ycombinator.com/item?id=13505287)

~~~
jdrov
There are a few key differences in our work. First, it's a very different
system; the prior experiments were done using trapped ions, and "defects"
(nitrogen-vacancy centers) in diamond, while our system used nuclear spins.
The more important difference is that our system is very ordered, since it
took place on an actual crystal lattice with a high degree of symmetry (this
matters because some theories proposed the need for this disorder to observe
the effect -- the trapped ion experiment even purposely included disorder).
This is the reason for our use of the word "ordered" in the title of the
paper.

Other differences include our further work to clarify the phemomenon,
including the creation of "echoes" to explore the coherence of the system (see
my other comments) among other new contributions about the parameter space and
behavior of the effect. Finally, it's just surprising to have observed this
effect across so many systems which are all so different from each other (very
different Hamiltonians).

------
ianai
Naively I’m imagining the flips are triggered via incoming particles -
photons? If so, what are the characteristics required of the inputs and how
does that affect the particles in/out of the system?

I’m wondering about possible applications for time crystals?

Anyway this is really intriguing! When I first read of time crystals they
really seemed unlikely to ever be observed. But if they’re in human made
crystals they just might be either more common or easier to produce than I’d
thought.

~~~
jdrov
We use a solenoid to drive magnetic fields in our sample (RF frequencies, near
field), but yes, we do often envision an absorption or emission event by a
given nuclear spin as it changes its spin state in the presence of an even
stronger, static magnetic field. We have to carefully match the frequency of
the driving magnetic field to the so-called Larmor frequency of the spins,
which allows them to absorb the supplied energy.

We're working on understanding possible applications now, and we also wonder
whether this is a more commonly available phenomenon than originally thought.
As experimentalists, we're very conservative in our claims -- for instance, we
explain our observation of the "DTC signature" specifically proposed by
theorists, without making claims as to the final interpretation of the results
for the existing theory. Instead, our job is to very clearly explain what we
did and what resulted, and then we get to see (and in some ways participate
in) how the broader condensed matter community comes to understand the
phenomena. It's an exciting position to be in, there are still many
interesting unknowns!

~~~
Steel_Phoenix
Is the timing of the crystal influenced by its size, shape, or composition?
Does it just double whatever the input signal is, or do you have to find a
particular resonant frequency? If you brought a ticking crystal into contact
with one that was not, or was ticking at a different frequency, would there be
transfer or loss? If you just charge up a corner of a crystal, does it extend
to the rest? Can you look for ticking in crystals you haven't charged, and if
so, are they readable long enough to be used for dating or information
storage?

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ams6110
Off-topic, but the name "time crystals" just sounds like something straight
out of a Doctor Who episode.

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greggarious
So what are the practical applications of a "time crystal"? The name certainly
allows the mind to run wild...

:)

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subcosmos
Does it have four-corner rotation?

[https://en.wikipedia.org/wiki/Time_Cube](https://en.wikipedia.org/wiki/Time_Cube)

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jonjojr
"Scientists say that understanding time crystals may lead to improvements in
atomic clocks, gyroscopes, and magnetometers, as well as aid in building
potential quantum technologies"

So you are saying that the Time Stone/Gem is real? How exciting!!!!

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thomble
Can I somehow integrate this with my 1982 DeLorean?

~~~
jdrov
Admittedly, if you asked me 20 years ago which one of "time crystal" or "flux
capacitor" were actually from a movie called "Back to the Future," I am _not_
confident I would answer correctly.

~~~
reificator
I hope that's because you were too young to have seen the movie, because 20
years ago was 1998.

Back to the Future was 1985. (And 1989/1990)

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w0mbat
Don't let Thanos get it.

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programminggeek
I'm still waiting for researchers to find a Time Cube.

~~~
neuromantik8086
Hold off- we need to find a Time Square first!

"The 4-equidistant Time points can be considered as Time Square imprinted upon
the circle of Earth."

I don't think it's this:

[https://upload.wikimedia.org/wikipedia/commons/4/47/New_york...](https://upload.wikimedia.org/wikipedia/commons/4/47/New_york_times_square-
terabass.jpg)

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thedorkknight
You could argue that all crystals travel through time

~~~
uvatbc
No argument there.

Hello readers from the future!

~~~
tenaciousDaniel
Hi, you from 8 minutes ago!

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lostmsu
He won't see your message :(

~~~
diegoperini
Who?

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killjoywashere
In other news, Timex remains in business and the Marvel Comics Universe will
be hiring the most photogenic of the three for "scientific consulting" on the
next 3 to 7 MCU films.

