aspuru-list April 2018

aspuru-list@lists.fas.harvard.edu

15 participants
40 discussions

[Aspuru-Guzik Group List] ITAMP lunch seminar - Daniel Greif, Harvard University (April 26th)

by Bekenstein, Rivka

*ITAMP Lunch Seminar* *Speaker: *Daniel Greif (Harvard University) *Date:* Thursday, April 26th *Time:* 12:00-1:00 pm Includes Pizza. *Title: *New Frontiers in Fermionic Quantum Gas Microscopy *Abstract: Quantum gas microscopy of ultracold fermionic atoms in optical lattices allows studying strongly correlated low-temperature phases in the Hubbard model. Through an entropy redistribution technique we have demonstrated long-range antiferromagnetic order extending over our entire sample, a disk spanning ten sites across filled with a two-component spin mixture of ultracold fermionic Li-6 atoms in a square lattice. Our microscope provides access to quantities such as the site-resolved spin correlation function, spin structure factor, and full counting statistics of the staggered magnetization. By hole doping the system away from half-filling we explore regimes of the Hubbard model phase diagram where precise numerical studies become challenging. We study the interplay between hole motion and the antiferromagnetic order: when a hole tunnels in an antiferromagnet, it can distort the surrounding order and form a string. This could be an essential aspect of high-temperature superconductivity in cuprates, and the readout of our microscope allows us to directly address this question. Besides discussing our current progress in this direction, I will also explain a new cooling technique based on quantum engineering of ultra-low entropy band-insulators to obtain even lower temperature states.* *Location: *B-106 @ Center for Astrophysics (60 Garden Street) *Directions: *After entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, B-106 will be at the end of the hallway on the left side.

6 years

[Aspuru-Guzik Group List] Reminder: Felix's Last Day, April 30th & Siria On Vacation May 1-16.

by Siria Serrano

Group, A quick reminder that Felix's last day with the group is next Monday, April 30th and I will be on vacation and unavailable May 1-16. *Finally, we are having breakfast together this Friday, April 17th 10:30 AM in the Division Room so be sure to swing by and celebrate Felix!* Cheers, Siria -- *Siria Serrano* *Faculty Assistant* *Aspuru-Guzik Group* *Harvard University **Department of Chemistry and Chemical Biology* *12 Oxford St. M 136* *Cambridge, MA 02138* *P:** (617) 496-1716 <%28617%29%20496-1716>** F: **617-496-9411 <617-496-9411>*

6 years

[Aspuru-Guzik Group List] [qip] more talks next week

by Aram Harrow

Dear quanta, On Wed, there are a few talks at this meeting which should be of interest to many of us. http://physicsrisingstars.mit.edu/agenda Both are in 4-349. 9am: "Tests of Quantum Measurement with Superconducting Qubits" Sydney Schreppler, UC Berkeley 11:30am: "Quantum Steampunk: Quantum Information and Thermodynamics" Nicole Yunger Halpern, California Institute of Technology -aram _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

6 years

[Aspuru-Guzik Group List] [qip] One more talk today

by Aram Harrow

Mark Wilde will give a short talk at 3:30 in 6-310. Title: Union bound for quantum information processing Abstract: Gao’s quantum union bound is a generalization of the union bound from probability theory and finds a range of applications in quantum communication theory, quantum algorithms, and quantum complexity theory [Phys. Rev. A, 92(5):052331, 2015]. It is relevant when performing a sequence of binary-outcome quantum measurements on a quantum state, giving the same bound that the classical union bound would, except with a scaling factor of four. In this paper, we improve upon Gao’s quantum union bound, by proving a quantum union bound that involves a tunable parameter that can be optimized. This tunable parameter plays a similar role to a parameter involved in the Hayashi-Nagaoka inequality [IEEE Trans. Inf. Theory, 49(7):1753 (2003)], used often in quantum information theory when analyzing the error probability of a square-root measurement. An advantage of the proof delivered here is that it is elementary, relying only on basic properties of projectors, the Pythagorean theorem, and the Cauchy– Schwarz inequality. As a non-trivial application of our quantum union bound, we prove that a sequential decoding strategy for classical communication over a quantum channel achieves a lower bound on the channel’s second-order coding rate. This demonstrates the advantage of our quantum union bound in the non-asymptotic regime, in which a communication channel is called a finite number of times. Joint work with Samad Khabbazi Oskouei (Islamic Azad University) and Stefano Mancini (University of Camerino) _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

6 years

[Aspuru-Guzik Group List] [qip] group meeting today

by Aram Harrow

Dear quanta, We will meet at 11am in room 6-310. Urmila Mahadev will talk at 1:30pm in room 6c-442. We will also have various visitors around for the day; besides Urmila, there is Kristan Temme, Ashley Montanaro and Mark Wilde. You are encouraged to track them down if you want to meet with them. Mark will only be around in the afternoon. -aram _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

6 years

[Aspuru-Guzik Group List] No group meeting tomorrow (ChemRxiv)

by Ian Kivlichan

Hi all, Because of the conflict with the ChemRxiv talk, we won't have group meeting tomorrow. We'll pick back up next week with a talk from Pascal. All the best, Ian

6 years

[Aspuru-Guzik Group List] Three dinner spots with Marshall Brennan of ChemRXiV fame.

by Alan Aspuru-Guzik

Group members, If you are interested in having dinner with Marshall Brennan who runs the ChemrXiV, just reply to this email ASAP. The first 3 that do so will get to meet him for dinner tomorrow. He and you can follow up. I will be out of town so I will miss it, but I hope you all have fun. He is the leader of open access in chemistry in the world, IMHO. Copying him! Alan Alán Aspuru-Guzik | Professor of Chemistry and Chemical Biology Harvard University | 12 Oxford Street, Room M138 | Cambridge, MA 02138 (617)-384-8188 | http://aspuru.chem.harvard.edu | http://about.me/aspuru

6 years

[Aspuru-Guzik Group List] Group Photo

by Mendoza, Douglas

Dear all, We will be taking our group photos tomorrow, Wednesday 18th, at 1:15pm. Let's meet outside the group's administrative offices. Forecast for tomorrow seems okay, hopefully we'll get some nice shots. Please try to be on time so we can be done by 1:20 and go back to our busy schedules. Thanks, Douglas

6 years

[Aspuru-Guzik Group List] [qip] Thesis Defense on April 25th

by Kevin Thompson

Hi all, My apologies if you receive this email twice. I will be defending my thesis in LISE 303 (at Harvard) on April 25th at 10 am. Refreshments will be provided. The talk will be roughly half material Ive talked about at group meetings/seminars and half some new results concerning the construction of unitary 2 designs. *Abstract * The existence of quantum locally generated codes is a long standing open problem in quantum information theory. In this thesis, we consider a bound concerning this conjecture as well as a few constructions with codes that are 'barely non-local'. First we formulate and analyze a bound concerning the possible topologies of locally generated codes. It is well known that quantum codes which can be defined on lattices (geometrically local codes) must have sub-linear distance, and hence must be bad quantum codes. We establish a complementary result to this one, and show quantum codes which are strongly not embeddable into finite dimensional lattices must also have poor distance. Along the way we derive some results concerning "pseudorandom" classical codes. Given that quantum codes seem to be difficult to construct, it seems useful to examine "bad" quantum codes for applications in information and communication. Indeed, most of the work in quantum error correction by researchers today is in this direction. We construct a nearly local quantum erasure code which can achieve the capacity of the quantum erasure channel. This code has very poor (adversarial) distance, but still manages to correct random erasure errors with high probability. The codes use random Erdos-Renyi graphs to construct quantum states which are nearly local, but also highly entangled across fixed cuts with high probability. We derive some new results concerning classical codes with log-sparse parity check matrices which may be of independent interest. Inspired by this construction, we are able to construct new approximate unitary 2-designs or scramblers. The study of scrambling is the study of the mixing properties of different distributions of random unitaries. There is an inherent duality between the study of scrambling and the study of error correction: A good quantum code will make a good scrambler and vice versa. We study the scrambling properties of our random Erdos-Renyi graph state encoding circuits. We are able to show that these circuits, when supplemented by some local Expander Graph quantum circuits, form "weak" approximate unitary 2-designs with O(n log(n)) many gates and depth O(log(n)). This construction, strictly speaking, does not achieve more efficient parameters than existing approximate 2-designs (it matches them), but might have implementation advantages over other designs and points to a conjecture which could yield approximate unitary designs with time independent qubit-to-qubit coupling. This would be a very interesting construction in the context of experimental randomized benchmarking. Best, Kevin _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

6 years

[Aspuru-Guzik Group List] [qip] talk on Friday, Apr 20, 1:30pm, 6c-442

by Aram Harrow

Urmila Mahadev from Berkeley will talk about her recent breakthrough. title: Classical Verification of Quantum Computations. abstract: We present the first protocol allowing a classical computer to interactively verify the result of an efficient quantum computation. We achieve this by constructing a measurement protocol, which enables a classical verifier to ensure that the quantum prover holds an n qubit quantum state, and correctly reports the results of measuring it in a basis of the verifier's choice. This is enforced based on the assumption that the learning with errors problem is computationally intractable for efficient quantum machines. The talk will be an informal blackboard talk that will focus on the technical details and will not dwell on the motivation and broader context. _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

6 years

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aspuru-list April 2018