June 1, 2008

Adventures in fume hoods

Posted by Arcane Gazebo at 7:03 PM

I'm still occupied with other activities (like unpacking boxes, and discovering just how many bugs I can inadvertently cram into 100 lines of perl), but in the absence of blogging I invite you to enjoy the latest PhD Comics strip on fume hoods.

This rings especially true since my lab in grad school needed a fume hood only occasionally, and therefore had only one which sat mostly neglected in the fabrication lab. This made it a fantastic storage closet for unknown chemicals until somebody actually needed to use it for science, at which point hazmat teams would need to be called. (Note to Berkeley EH&S: joking!)

In contrast, the most hazardous chemical at my new job is the curry from Teriyaki Boy, a.k.a. "The Yak". (Angelenos: Picture the Japanese-food equivalent to Tommy's chili.)

November 30, 2007

Just call it entropy research

Posted by Arcane Gazebo at 10:07 AM

I thought our lab was a mess, but it could be worse... via Chad Orzel, here's a chemistry professor (at UT San Antonio) whose lab had to be forcibly cleaned by the university:

"Clean your room or get out!" Words from a frustrated parent to a messy teenager? Not quite. The mess-maker in this case was a chemistry professor at the University of Texas, who ignored repeated warnings to clean up his dangerously cluttered lab space. When University officials decided to clean it themselves, the professor caused such a disturbance that campus police had to lead him away in handcuffs. The professor was eventually fired, which prompted a lawsuit claiming that the University retaliated against him and denied him equal protection.

The legal opinion notes that apart from the problems in the lab, the professor's office was an "extreme fire hazard", which still puts him a step below the physics professor here at Berkeley who actually set his office on fire. In any case, this makes me feel better about the disordered state of our lab. We cleaned it only a few months ago but it returns rather rapidly to equilibrium.

(I also want to point out that the legal blogger linked above is evidently a fan of Arrested Development, and has chosen the obvious pseudonym to use on his law blog...)

December 7, 2006

Overheard in the Lab

Posted by Arcane Gazebo at 3:10 PM

"The fume hood's gone from suck to blow!"

Permalink | Tags: Lab

November 30, 2006

Publication: Solid-State Qubits with Current-Controlled Coupling

Posted by Arcane Gazebo at 2:29 PM

As some of you know, we recently had a paper accepted to Science. The paper appears in the latest issue, and is now available online.

I will try to post something in the next few days that explains these results for the non-physicists in the audience. In the meantime, there's this post from March about these experiments (from before we had the major findings), and here's the abstract:

Solid-State Qubits with Current-Controlled Coupling

T. Hime, P. A. Reichardt, B. L. T. Plourde, T. L. Robertson, C.-E. Wu, A. V. Ustinov, John Clarke

The ability to switch the coupling between quantum bits (qubits) on and off is essential for implementing many quantum-computing algorithms. We demonstrated such control with two flux qubits coupled together through their mutual inductances and through the dc superconducting quantum interference device (SQUID) that reads out their magnetic flux states. A bias current applied to the SQUID in the zero-voltage state induced a change in the dynamic inductance, reducing the coupling energy controllably to zero and reversing its sign.

Permalink | Tags: Lab, Physics, Publications, Quantum Information, Science

September 2, 2006

Clarke group research in Physics Today

Posted by Arcane Gazebo at 7:35 PM

I'm late noticing this, but the August issue of Physics Today has an article (subscription required) about axion detection experiments, which mentions some work being done in the Clarke group:

An amplifier whose noise temperature approaches the quantum limit would dramatically improve the sensitivty and search rate of the axion experiment. To achieve that goal, our collaborator John Clarke and his coworkers at the University of California, Berkeley, developed a new amplifier based on a microstrip-coupled superconducting quantum interference device in 1996. Unlike the noise behavior of heterojunction transistor amplifiers at low temperatures, the intrinsic noise of the SQUID is proportional to the physical temperature, the origin being thermal noise in shunt resistors across the SQUID's Josephson junctions. Cooling reduces the noise until it flattens out within 50% of the quantum limit. Newer SQUID designs with micro-cooling fins that enhance the coupling of electrons to the lattice are pushing these devices closer still to the quantum limit.

Unfortunately the full article is only available to subscribers, but those of you who are APS members can check it out. The quantum-limited amplifier is pretty cool and some groups are looking at using it for qubit experiments as well. Ironically, the vacuum pumps required to cool this low-noise amplifier are really loud, and so having to work in the same room as this experiment is sort of annoying.

Permalink | Tags: Lab, Physics, Science

August 24, 2006

Rough Superconductor

Posted by Arcane Gazebo at 3:53 PM

Niobium is a metal that we frequently use here for its superconducting properties (Tc = 9.3 K). At lunch today we were wondering where it comes from: are there niobium mines somewhere? Perhaps, I suggested, it is mined in Africa under highly exploitative conditions, and we'll find protestors picketing the lab for our use of blood niobium.

Turns out this is disturbingly close to the truth:

Coltan is the colloquial African name for (columbite-tantalite), a metallic ore comprising niobium and tantalum.


Coltan smuggling has also been implicated as a major source of income for the military occupation of Congo. To many, this raises ethical questions akin to those of conflict diamonds. Owing to the difficulty of distinguishing legitimate from illegitimate mining operations, several electronics manufacturers have decided to forgo central African Coltan altogether, relying on other sources.

On the other hand, it looks like coltan is more important as a source of tantalum, and most niobium comes from Brazil and Canada. So probably our research isn't built on slave labor and exploitation (postdoc salaries aside).

Permalink | Tags: Lab, Physics, World

August 22, 2006

Types of laboratory scientists

Posted by Arcane Gazebo at 11:49 PM

Via Syaffolee, an over-the-top but amusing list of personality types one encounters in a science lab. In fact, I believe I've met most of these people. I've put a lot of effort into not becoming #5 (the obsessive perfectionist with no life), but this probably just makes me closest to #1 (the antisocial weirdo)—although my personal hygiene isn't that bad and I've been more social lately. Of course it's not an exhaustive list, so maybe I need to add to it:

7. The Blogger
He seems quiet, but he's actually telling the world about the latest lab mishaps on the Internet. These scientists prefer highly automated experiments so as to spend more time surfing the web. They're good with computers and publicizing results to a broad audience. They are communicative provided the medium is e-mail or IM, and happy to come to parties if there's a proper Evite or MySpace announcement. If the network goes down they are likely to display withdrawal symptoms.

Permalink | Tags: Academia, Lab, Science

August 15, 2006

Measurements of gravity using cryogens [Updated]

Posted by Arcane Gazebo at 7:00 PM

This is what Chad Orzel refers to as a True Lab Story:

Condensed matter labs such as ours receive frequent deliveries of liquid nitrogen in one- or two-hundred liter dewars. Unfortunately, most of the Berkeley cond-mat labs are in Birge Hall, which has no loading dock, so that the LN2 dewars arrive on the first floor of neighboring LeConte where they must be wheeled over to their destination by some low-seniority student. Since the Berkeley campus is on a hill, the loading dock at the back of the building is one floor higher than the other entrances to LeConte and all the entrances to Birge. One can push the dewar around the outside of LeConte, but a shorter route is to take the elevator down one floor and go out the side door.

Yesterday the LeConte elevator was out of order, which for most of us would have meant taking the long way around. However, one undergrad, tasked with transporting a full 230L dewar, simply decided to take the stairs.

At about 80% the density of water, 230 liters of liquid nitrogen weighs about 400 pounds, not counting the additional weight of the steel vessel containing it. When rolled onto the stairs, the dewar promptly tipped over and plummeted downward on its side, knocking deep gouges in the marble steps and dragging along the unfortunate student, who inexplicably held on as his cargo began to tumble. Miraculously both student and dewar arrived at the landing without rupturing, but the dewar was still on its side and pressure was building up.

This was the situation when we got the frantic call from the building manager; once enough of us arrived at the scene we were able to pull the dewar upright and release the pressure. This averted any imminent explosion, but now we had a different problem: 400 pounds of liquid nitrogen stranded on a landing between the ground and first floors. Suggestions were floated including emptying the nitrogen out the nearby window, but ultimately we found another dewar which was wheeled to the top of the stairs on the first floor, and the nitrogen was transferred there through a long hose. The empty dewar was then carried up the stairs, a task requiring four men and gouging new (but shallower) grooves in the staircase.

Recalling what happens when a LN2 cylinder does rupture, it's the general consensus that this student is lucky to have survived and LeConte Hall is lucky to still have a staircase.

Photos below the fold [updated with photo of wall damage]:

Continue reading "Measurements of gravity using cryogens [Updated]"
Permalink | Tags: Lab, Photos, Physics, Science

July 21, 2006

Friday Lab Blogging: Proper Laboratory Attire

Posted by Arcane Gazebo at 12:01 PM

Safety is a major concern in any lab, and in this group we are very dedicated to maintaining a safe environment. We are so dedicated that our last safety warden left to become a Buddhist monk. We'll see how long the next one lasts.

Some processes, such as silvering glass dewars, are sufficiently hazardous to alarm even the most reckless among us, and so we have assembled an appropriate set of gear, modeled below by Iskander:

safety boy

The stylish yellow lab coat, with detachable hood for the emo hoodie look, is flame- and acid-retardant, perfect for handling the fulminate byproducts of the silvering process. The face shield adds that edgy "riot gear" touch, but since a face shield only qualifies as secondary eye protection it is complemented by an elegant pair of safety goggles. Heavy gloves complete the outfit, removing any possibility that one might handle something delicately and thereby avoid the inevitable explosion.

Chemists in the audience are welcome to mock our misplaced concern and/or one-up us with stories of yet more elaborate lab outfits.

Permalink | Tags: Lab, Photos

June 13, 2006

Helium is the sweetest of the noble gases.

Posted by Arcane Gazebo at 4:12 PM

Slate worries about the dangers of helium. Yes, innocent, inert helium. Apparently, you might pass out and hit your head on something. Maybe next Slate will do an article on the threat of the liquid phase, on the grounds that it's really cold. I once took a spray of liquid helium full in the face—it was cool and refreshing!

Permalink | Tags: Lab, Randomness, Science

April 4, 2006

Innovations in Masculinity Quantification

Posted by Arcane Gazebo at 9:33 PM

Chad Orzel directs us to Dylan Stiles, who demonstrates what bored Stanford chemists do with laboratory equipment. The Man-O-Meter Challenge is unlikely to catch on in this lab, since most of our pressure gauges are permanently attached to vacuum systems, and don't measure overpressure anyway. However, considering my winning record at Lloyd House blow-pong, I expect I would do quite well at this. (This is probably not something I should admit.) I wish I had a comparable story to tell from our lab, but while we have been known to misuse tools such as the implement we refer to as the Grabby Hand of Science, we've never accomplished a repurposing quite as interesting as the Man-O-Meter.

Also, I don't think I'd heard the term "manometer" before; we always just say "pressure gauge". Is that nomenclature a chemistry thing?

Permalink | Tags: Lab, Science

March 22, 2006

Workplace Physics

Posted by Arcane Gazebo at 10:09 PM

Classical theory: I tend to occupy either my office on the first floor or the lab in the second basement. Obviously the office has the higher potential energy. By the work-energy theorem, I can be promoted to the higher-energy state by performing work on the system. Once I am up in the office, I write up the results of the experiment and the energy exits the system in the form of a publication, so I find myself back in the lab.

Quantum theory: My state oscillates between the lab and office levels. Timescales for transitions are on the order of several weeks. Spontaneous absorption of data will cause a transition to the office state; the office state will randomly decay into the lab state with emission of one quantum of data (a PRL submission). My state is entangled with the state of the dilution refrigerator: if I am observed in lab there is a very high probability that the fridge is running.

A thermodynamic digression: When I am away from my office for several weeks, the number of objects on my desk increases with time. When I am away from the lab for several weeks, the number of items in the lab decreases with time (roughly in proportion to their utility to other members of the group). Conclusion: the chemical potential in the lab is positive, while the chemical potential on my desk is negative.

Permalink | Tags: Lab, Life, Physics

March 9, 2006

Innovations in LN2 Storage

Posted by Arcane Gazebo at 11:13 AM

It sounds like an Aggie joke: a Texas A&M chemistry lab had a liquid nitrogen tank with a leaky pressure relief valve, so some clever individual solved the problem by replacing the valve with a metal plug. This ultimately transformed the chemistry lab into a rocketry lab.

The cylinder had been standing at one end of a ~20' x 40' laboratory on the second floor of the chemistry building. It was on a tile covered 4-6" thick concrete floor, directly over a reinforced concrete beam. The explosion blew all of the tile off of the floor for a 5' radius around the tank turning the tile into quarter sized pieces of shrapnel that embedded themselves in the walls and doors of the lab. The blast cracked the floor but due to the presence of the supporting beam, which shattered, the floor held. Since the floor held the force of the explosion was directed upward and propelled the cylinder, sans bottom, through the concrete ceiling of the lab into the mechanical room above. It struck two 3 inch water mains and drove them and the electrical wiring above them into the concrete roof of the building, cracking it. The cylinder came to rest on the third floor leaving a neat 20" diameter hole in its wake. The entrance door and wall of the lab were blown out into the hallway, all of the remaining walls of the lab were blown 4-8" off of their foundations. All of the windows, save one that was open, were blown out into the courtyard.

Fortunately no one was working in the lab at 3 am when it went off, so no one was hurt. However, this certainly redefines the concept of blowing up the lab. I'll have to keep this story in reserve in case I need to explain an accident to my advisor. "Did you hear about the guys at A&M who plugged their nitrogen tank and destroyed the building? Aren't you glad I only broke a vacuum pump?"

Via Uncertain Principles.

Permalink | Tags: Lab, Science

February 12, 2006

Climate Control

Posted by Arcane Gazebo at 3:41 PM

While the East Coast is buried in snow and Southern California struggles under a scorching heat wave, it's been 65 and sunny all week here in Berkeley. And we'll get the same weather in July. With this kind of climate, one might expect that the heating and air conditioning needs of a campus building like Birge Hall would be pretty minimal. And indeed, through efficient design the building is maintained at a pleasant environment with hardly any energy.

Ha! I'm joking, of course. What they actually do here is run the heating and the air conditioning at the same time so that they cancel out. I only discovered this fact this week, when the heat pump broke—leaving the air conditioning running unchecked. Naturally there's no way to adjust it, and so I end up carrying a sweater to lab with me, so that after walking through perfect weather to get there I can bundle up when I enter the building and avoid freezing to death.

Somehow, you'd think a physics building would have a more efficient solution to the problem of temperature control, but maybe it's a corollary to the fact that the architecture building is always the ugliest building on campus. It brings to mind a common method of temperature control in condensed matter physics: cool the sample down to 4.2K with liquid helium, and then use an electric heating element to warm it back up to the desired temperature. But I'm not sure it scales up as well as the designers of Birge Hall's HVAC system seem to believe.

Permalink | Tags: Berkeley, Lab, Life, Physics, UC Berkeley

January 26, 2006

Experimenting on my own software

Posted by Arcane Gazebo at 3:16 PM

On the software I use to run our qubit experiments, there is a checkbox labeled "Inverted Pulses". Two or possibly three years ago I added this feature to the software, so that the option is available to operate our readout scheme under the opposite electrical polarity. Normally our readout pulses go to positive voltage, but occasionally it is interesting to see what happens with negative voltage pulses. Ideally the behavior should be completely symmetric, but in practice there are asymmetries that should generate different results.

But when I say "occasionally" I mean very occasionally; to the best of my recollection I used this feature for a couple of days after I installed it, and then never checked the box again. In the meantime I have added many other features to the increasingly bloated software, without caring very much whether they were compatible with the rarely-used inverted pulses. Of course, this has all come back to haunt me now that I again want to reverse the polarity on the readout pulses, and am faced with the question: Does the "Inverted Pulses" box still work?

After some testing it's clear that the answer is "no", and furthermore it's not obvious why it ever worked. (The crucial command to the instrument contained a syntax error!) Or maybe it didn't ever work and I had forgotten this, or it was one of those pieces of software I wrote anticipating a potential experiment and then never actually used. I seem to have fixed the bugs, but there are still some quirks in the startup sequence that should probably be ironed out...

(Since my former CS 1 TA reads this, I will remark that these problems could be avoided with properly documented and tested code. Ha! Unfortunately, the culture of experimental physics does not value properly documented and tested code. The culture of experimental physics values code which can be produced five minutes after a postdoc says, "Wouldn't it be interesting to try [a complicated new pulse sequence while sweeping over three separate parameters]?" And so three years later I'm looking at my own software wondering what the hell that switch does.)

Permalink | Tags: Lab, Life, Science, Technology

January 21, 2006

Experimentalist bloggers and Joule heating

Posted by Arcane Gazebo at 10:50 PM

Yesterday Chad Orzel speculated about the relative absence of experimental physicists in the blogging community. Unfortunately, I didn't have time to comment until now, because I was busy working in the lab. (Actually we were gearing up for, and then undergoing, a major safety inspection. The inspectors, who were reminiscent of the consultants from Office Space, stood around trying to invent scenarios under which a graduate student could suffer oxygen deprivation folowing sudden helium vaporization in our dilution fridge.)

Anyway, Chad's hypothesis was that theorists spend more time in front of computers on a daily basis, and thus blogging is just more convenient. This seems right to me: I'm one of the few condensed matter experimentalists who maintains a blog (and it probably helps that I'm a grad student rather than a postdoc or on the tenure track), and whether or not I have time to post mostly depends on how much time I'm spending on the computer, versus in front of an oscilloscope or soldering iron (or bolting power strips to desks two feet above the floor to satisfy safety inspectors).

For a period of about 10 months last year, we did not have an experiment running as we were fabricating a new sample. And due to the division of labor among the grad students on this project, I was not closely involved with the fabrication process, and instead spent my time reading papers, writing papers and reports to funding agencies, writing software, designing circuits, and doing simulations. These were all computer-intensive activities, and I was able to get a fair amount of blogging done. For the last two months, however, we've been doing measurements on the chip we made last year, and I've spent a lot of time taking data, looking at scope traces, and reconfiguring wiring. Hence, I think up a bunch of posts over the week and write them up on Saturday night, which is a bit lame.

Fortunately, I do frequently have the ability to post even under these conditions, due to the phenomenon of Joule heating: if a current I is applied to an electrical resistance at a voltage V heat will be dissipated at a rate equal to the product IV. Every time we make a measurement, we apply a current pulse to our device, which produces a voltage and a corresponding amount of heat. If this heat is allowed to accumulate on the chip, it will wipe out the quantum effects we're trying to study, so between each measurement we have to wait long enough for the chip to cool off. In practice, this means instead of taking a million measurements in a second we are reduced to about 2,000. Furthermore, to get good statistics and sweep over an interesting range of parameters we have to take a large number of measurements, so it turns out that to get interesting results we need to measure continuously for at least 12 hours. I've written an overly baroque computer program to automate all this, so once I know what I want to measure, I can push a button to start the experiment, do something else for a while (usually analyzing data from the previous run), and then collect all the data hours later (or the next day). (This is only when everything is working properly; otherwise it's back to the oscilloscope and wiring diagrams.) And in the gaps I can do a little blogging.

These days, the trend in the superconducting qubit community is towards nondissipative readout—i.e., measurements which leave the device in the superconducting state and thus produce no heat. This might threaten to take away my blogging windows, except that it would also enable measurements that require even better statistics and broader sweeps, and so there will still be reasons to do 12- and 24-hour runs. (Actually, our record is about 48 hours, but we don't currently have the battery life to repeat that.)

Permalink | Tags: Lab, Life, Physics, Quantum Information, Science

November 14, 2005

Clarke group research in ScienceMatters@Berkeley

Posted by Arcane Gazebo at 6:25 PM

My advisor was profiled in the latest issue of ScienceMatters@Berkeley, an online UCB publication written by Boing Boing's David Pescovitz. Most of you know about my work on the qubit project; the ScienceMatters article also covers some of the other research in the group.

UPDATE: It's pretty cool to see one of our figures on Boing Boing, even if it is from the (admittedly more photogenic) MRI project rather than the qubit research.

Permalink | Tags: Lab, Physics, Publications, Science, UC Berkeley

October 7, 2005

Expensive Solitaire Console

Posted by Arcane Gazebo at 5:14 PM

My advisor has a powerful dislike of digital electronics, partly due to the additional electrical noise generated by such circuits. Another issue is that manufacturers of high-precision digital equipment are often tempted to add dubious "enhancements" to their products. Consider, for example, our Tektronix digital oscilloscope. It has a lot of useful features, most importantly a 1 GHz bandwidth. On the other hand, it runs Microsoft Windows.

Now, this does allow me to play solitaire during an extended measurement. And in principle the ability to run programs like Labview could be very useful, and the scope connects to the network very easily. On the other hand, this means that the software that actually runs the core oscilloscope functions is Windows software.

Recently, when booting up the scope, the aforementioned software has been exiting immediately with an "unrecoverable system error". This effectively converts the instrument into an ordinary PC with a tiny screen (and a $30,000 price tag). This was the first time I have attempted to repair a scientific instrument by reinstalling Windows. Unfortunately, this had no effect on the problem, leading me to guess that it was a hardware malfunction on the acquisition board. Time to run the scope diagnostics... which only exist inside the software that refuses to run.

So we're sending the thing to Tektronix where they will repair it for a hefty fee. Meanwhile, I am starting to appreciate the simplicity of purely analog electronics.

Permalink | Tags: Lab, Science, Technology

September 13, 2005

The Road to Pretentious Music Geek Hell, Part the Second

Posted by Arcane Gazebo at 12:30 PM

I'm not one of those people who prefers to listen to vinyl records. But after learning that the vinyl edition of the Decemberists' Picaresque will have five bonus songs, I kind of wish I were.

There is actually a record player in the lab, possibly even operational (its radio tuner still works at least). So I could start buying vinyl music to listen to while doing experiments. My advisor's always worried about noise generated by digital electronics, so presumably he'd approve of the analog approach, and there's an abundance of ADCs if I want to get those bonus songs into iTunes. Or I could go with my original plan of just plugging my iPod into the record player's auxiliary port.

Permalink | Tags: Lab, Music

August 22, 2005

Follow-up on decoherence

Posted by Arcane Gazebo at 3:14 PM

One of the comments on the flux qubit post asked an important question: where does the decoherence come from? I dealt with this a bit in the thread itself, but this post will be a less technical treatment.

In general, decoherence is a result of the fact that the qubit under study isn't in isolation, but interacts with some larger environment. Through this interaction, information that starts out concentrated in the qubit dissipates out into the environment, and likewise information in the environment mixes into the qubit. Of course, the state of the environment isn't known beforehand so the information that mixes in just looks random, and averages out over a large number of experiments.

In the case of our qubit, what matters is the electromagnetic environment—the electric and magnetic fields that act on the qubit. Any fluctuations in these fields can produce decoherence, and just about everything produces some level of field noise.

Continue reading "Follow-up on decoherence"
Permalink | Tags: Lab, Physics, Quantum Information, Science

August 18, 2005

Publication: Flux qubits and readout device with two independent flux lines

Posted by Arcane Gazebo at 7:36 PM

This paper contains the major results of my graduate research so far, compressed into four pages. Instead of the abstract I'm posting something closer to a layman's explanation, which is below the fold since it got a bit long.

Flux qubits and readout device with two independent flux lines
B. L. T. Plourde, T. L. Robertson, P. A. Reichardt, T. Hime, S. Linzen, C.-E. Wu, and John Clarke
Phys. Rev. B 72, 060506(R) (2005)

Continue reading "Publication: Flux qubits and readout device with two independent flux lines"
Permalink | Tags: Lab, Physics, Publications, Quantum Information, Science