Kenneth Brown Profile picture
quantum information scientist Professor @DukeEngineering @DukeTrinity @DukeU Advisor @IonQ_Inc
Sep 25, 2020 19 tweets 10 min read
The @bacon-@PeterShor1 code project has been a great collaboration with Chris Monroe's group @JQInews and my group @DukeEngineering @DukePhysics @GTCSE. It is an amazing experiment with excellent control over 13 ions in a chain of 15 ions. Here is a thread about the theory. 1/n The first error correction code is a concatenation of two repetition codes by @PeterShor1 in 1995… 2/n
Aug 5, 2020 8 tweets 3 min read
I agree with @abe_asfaw and @crazy4pi314 that the Bloch sphere doesn't help that much understanding larger quantum systems. However, there is an interesting set of counter examples. The Bloch sphere needs two non-commuting Pauli matrices. Any two. They could be k-qubit Pauli matrices.
Aug 2, 2020 4 tweets 3 min read
Our paper on weighted union-find decoding on the toric code is now out in @PhysRevA… @Huang_Shilin first developed the weighted union-find decoder to look at the whole family of compass codes but using a slightly non-standard error model.
Jul 8, 2020 4 tweets 3 min read
Congratulations to Pak Hong (James) Leung for successfully defending his PhD on "Robust Ion Trap Quantum Computation Enabled by Quantum Control." @DukePhysics @DukeTrinity #DukeQuantum Image James had a great collaboration with @kalandsman9 @JQInews where James would invent pulses for two-qubit gates and Kevin would show that they worked in practice.
Jun 25, 2020 5 tweets 4 min read
The #SummerSTAQ 2020 lecture notes, recorded lectures, problem sets, and discussion sections are now all available openly here. Enjoy and think about joining as a student or lecturer for #SummerSTAQ 2021. Let me again thank this years lecturers: @quantum_aram (@MIT), Akimasa Miyake (@UNM), Peter Love (@TuftsUniversity), Chris Monroe (@JQInews, @IonQ_Inc ), Abhinav Kandala and David McKay (@IBMResearch, #IBMQ), and Casey Duckering @prof_chong (@EPiQCExpedition @UChicago )
Jun 6, 2020 7 tweets 2 min read
I am really sorry to hear this but in the spirit of Jon Dowling, I will retell my two favorite slightly irreverent Dowling stories. When I was a grad student QC funding was the wild west because nothing worked and the government was trying to see if anything worked. This ended in a strange way where some program calls were made and then mysteriously canceled right around when I became a postdoc 2003-4
Jun 1, 2020 7 tweets 3 min read
This week is also #DAMOP online.…

My students and postdocs are presenting work @DukeEngineering and collaborators @JQInews @EmoryChem @UCLA and @TempleUniv Talks by session
D03.00002 Efficient Coherent Error Cancellation in Ion Trap Quantum Computers by Hidden Inverses
May 20, 2020 17 tweets 6 min read
A thread on the Cirac-Zoller gate: why it is important and why it is never used. (1/n) In 1995, ions were clearly a good choice for a qubit. The internal states were known to be very coherent and are still used to this day to build incredibly precise atomic clocks (2/n).
May 13, 2020 9 tweets 10 min read
Happy to join in celebrating #NSF70 with my #NSFstories. As an undergraduate @univpugetsound at a small liberal arts college, I was unsure what graduate school would be like. Thanks to the @NSF REU at the @UMNews, I was able to join @VPRCramer's lab for the summer and see what grad school life was like at a research university. #SeeNSF
Apr 10, 2020 4 tweets 3 min read
New paper on a weighted Union-Find decoder for the toric code with @Huang_Shilin and Mike Newman ( #DukeQuantum @DukeEngineering A weighted Union-Find decoder increases the threshold for the Union-Find decoder but at what cost? In previous work with @Huang_Shilin ( on 2D compass codes, we predicted it should be quadratically slower.
Apr 10, 2020 4 tweets 3 min read
New paper on QCCD ion trap architectures for near-term devices (
A great collaboration with Prakash Murali (@MartonosiGroup) , @margmartonosi, & @DriptoDebroy (@DukePhysics). Paper accepted at @ISCAConfOrg. #DukeQuantum @DukeEngineering @Princeton In the ion trap community there is a bit of a divide between what is the right size of an ion chain. On the one hand, small ion chains have been shown to have incredible fidelities. On the other hand, long ion chains allow you to grow Hilbert space more easily.
Apr 9, 2020 9 tweets 4 min read
Simulating water on a quantum computer with @IonQ_Inc… As we all know quantum computers are currently small and do not solve chemistry problems better than a classical computer cluster.
Mar 23, 2020 20 tweets 3 min read
Exponents and Logarithms: A Tutorial Thread 1/n We are all familiar with addition
and multiplication
but somehow the US has done a poor job teaching its citizens exponents and logarithms 2/n
Mar 13, 2020 7 tweets 3 min read
Natalie Brown (@GTPhys), Andrew Cross (#IBMQ), and I posted a new paper on leakage errors in the surface code to the arXiv today. @DukeEngineering #DukeQuantum Natalie recently defended her thesis on leakage errors. First, she compared whether it was better to have a magnetic field sensitive qubit or a leaky qubit using the standard depolarizing error model for the leaky qubit interaction.
Mar 10, 2020 10 tweets 3 min read
❄️👨‍💻👩🏾‍🔬❄️New cold chemistry paper! Our theory collaborators @TempleUniv, Hui Li, Ming Li, Alexander Petrov, and Svetlana Kotochigova, explain the charge exchange rate for K + Ca+ -> Ca + K+ that Jyothi Saraladevi (@DukeEngineering) measured. Taking place at 200 mK (-273 C or -459 F), it is probably the coldest reaction on @DukeU campus but I would need to check with @DukeChemistry
Feb 3, 2020 4 tweets 3 min read
Leonid Pryadko ( @UCRiverside ) will discuss "Approaching truly maximum-likelihood decoding for quantum codes" at the #KavliQuantumCoffeeHour today at noon in Gross 318 @DukeEngineering Image Great talk building off work by @S_Flammia @harrow @dabacon @CVuillot @BenCriger @QuantumChambs ImageImage
Dec 30, 2019 6 tweets 7 min read
We are one week away from @QIP2020 and I am excited to hear more about cutting-edge quantum information processing. This year @DukeEngineering is well represented with 1 plenary talk, 2 contributed talks, and 5 posters #qip2020 #QuantumDuke. @QIP2020 @DukeEngineering Daily Guide to @DukeEngineering presentations @QIP2020

Poster 118 -N. Brown, M. Newman and KRB
Conditions for fault tolerance in the presence of leakage
Oct 23, 2019 5 tweets 1 min read
My Intro to Q. Eng. class today was supposed to cover ion trap gates. (We covered superconductor gates last week). The students demanded to hear about the Google experiment. I told them I would do a quick five minutes and we could cover it in more detail on Monday. 1 hr later the class ended. We covered the following items briefly: technical changes between Google Bristlecone and Sycamore (worked well with the material from last week), what are quantum sampling problems about and why are they hard classically, and the IBM simulation paper.
Apr 30, 2019 4 tweets 2 min read
Earlier this month I was quoted in @cenmag about ion trap quantum computers. Image Two years ago, I was quoted in @cenmag about materials simulations on near-term devices. Image
Apr 27, 2019 4 tweets 2 min read
New paper examining circuit level error models for error correction circuits composed of qubits that leak and noisier qubits that don't leak. We find that for a physically motivated leakage model, a mixture of qubits works best. This paper is the third in a series.
In paper 1, Natalie Brown and I compared two types of ion qubits (hyperfine=leaky, Zeeman=noisy) for toric codes using a standard leakage model. Zeeman wins for low magnetic field noise.
Apr 18, 2019 7 tweets 3 min read
In 2010, I was part of a Phase 1 @NSF Chemical Center for Innovation based out of @PurdueChemistry and led by Sabre Kais. The team was Sabre, Daniel Lidar, Peter Love, and @A_Aspuru_Guzik .