Please join us for this week's Quantum Gathering this Friday, 5/31. Dr. Siyuan Niu, who is a postdoctoral scholar at Lawrence Berkeley National Laboratory, will give a 20 minute spark talk entitled "Quantum circuit resizing for resource optimization.” The spark talk will be in Campbell 131 at 3:30 pm. After the talk we will continue with Mediterranean platters on the terrace. 

Please join us for this week's Quantum Gathering Friday, 5/17. Dr. Bart Andrews, who is an SNSF Postdoctoral Fellow at UC Berkeley working with Mike Zaletel and Rahul Roy on tensor network methods for quantum computing, will give a 20 minute spark talk entitled "Efficient simulation of fermionic quantum circuits using matrix product states.” The Gathering will take place in 131 Campbell hall with food and drink afterwards on the terrace.

Please join us for the final AMO/QI seminar of the semester featuring Dr. Michael Mills of Quantinuum. He will be giving a talk titled: Benchmarking a racetrack trapped-ion quantum processor

Abstract:
The System Model H2, a quantum charge-coupled device (QCCD) trapped-ion system with a new racetrack-shaped trap, is Quantinuum's latest generation of quantum computers. The new system successfully incorporates several technologies crucial to future scalability, including electrode broadcasting, multi-layer RF routing, and magneto-optical trap (MOT) loading, while maintaining, and in some cases exceeding, the gate fidelities of previous QCCD systems.

We describe the operations in the H2 system and benchmark the performance of primitive operations, including single-qubit and two-qubit gate fidelity, state preparation and measurement fidelity, and crosstalk errors. Further, we highlight several applications using the H2 system, such as the creation of non-abelian topological order and anyons. Finally, we discuss upgrades to the H2 system.

We would like to invite you to this week's Quantum Gathering for this Friday, 4/26. Dr. Johannes Mitscherling will give a 20 minute spark talk entitled "Quantum geometry - a unifying perspective towards understanding quantum materials.”The spark talk will be in Campbell 131 at 3:30 pm. After the talk we will continue with freshroll sandwiches on the terrace.

Please join us for this week’s AMO/QI seminar to celebrate Dr. Neil Glikin’s completion of his dissertation! After his talk there will be a celebratory lunch. Here is a zoom link in case you cannot attend in person.
He will be giving a talk titled: Creating and Destroying Rotational Coherence with Trapped Ions

Abstract:
Far from being just qubits, trapped ions are also near-ideal quantum harmonic oscillators thanks to their external motion. Over the past few decades, researchers have engineered oscillator motion into a wide variety of interesting, exotic, and useful nonclassical states. This talk is centered around a system which fundamentally deviates from this usual situation: By allowing ions to physically rotate around one another, their motion becomes rotor-like rather than oscillator-like. The key to realizing this system is a surface-electrode ion trap which is highly circularly symmetric. Our trapped-ion rotor carries the promise of unlocking a new rotor-based category of experiments. I will discuss how we prepare the quantum state of the rotor, in particular how we create coherent superpositions of angular momenta. I will also discuss how we have used this system to systematically probe the open quantum dynamics of a rotor interacting with its environment. Here, we have observed for the first time simple scaling laws for rotor decoherence. Finally, I will discuss a proposal for an experiment in which one can directly observe the consequences of exchanging a pair of identical particles. This will be done by superposing a reference state with one in which the particles have rotated by pi radians relative to each other.

Join us on April 19, 2024 in Campbell 131 at 2:30 pm to hear from Irfan Siddiqi and Andrew Jordan regarding their textbook, Quantum Measurement: Theory & Practice. We will also be giving away copies of their textbook. Afterward, join us outside for boba and empanadas.

Please join us for this week’s AMO/QI seminar featuring Dr. Jon Simon, Stanford. He will be giving a talk titled: Racing to the Bottom: Low Finesse, Small Waist Cavity QED

Abstract:
In this seminar I’ll tell the story of cavity quantum electrodynamics (cQED) from first principles, building towards a new type of sub-micron waist resonator recently developed in the Simon/Schuster collaboration at Stanford. We will start by developing physical intuition for cooperativity, the figure of merit that controls performance of light/matter coupled systems including photon collection efficiency, cavity-mediated information exchange fidelity, and even coherence of interactions of photonic quasi-particle. Maximizing cooperativity will push us in either of two directions; (1) high finesses or (2) small mode waists. The high-finesse route is well explored by many leaders in the field of cQED, so I will emphasize the quest to small mode waist resonators, motivating near-concentric resonators, bow-tie resonators, and finally, our lens cavities. These lens cavities sport mode waists below a micron, entering the strong coupling regime at finesses well below 100. I’ll share preliminary data demonstrating single-atom coupling to such a cavity, and a test-bench demonstration of an array of small waist cavities that we intend to integrate with an atom array.

Please join us for this week’s Spark talk featuring a presentation by Dan Carney, who is a theoretical physicist and staff scientist at Berkeley National Lab. He will giving a talk entitled "Some attempts to break quantum mechanics.”

The spark talk will be in Campbell 131 at 3:30 pm. After the talk we will continue with Mediterranean platters on the terrace.

Then join us after the talk on the patio for FOOD as well as beverages and continued conversation.

Please join us for this week’s AMO/QI Seminar for Dr. Jermey Axelrod’s Dissertation Celebration! Congratulations!! He will give a talk titled: A Laser Phase Plate for Transmission Electron Microscopy

Abstract: 

Low image contrast is a major limitation in transmission electron microscopy, since samples with low atomic number only weakly phase-modulate the illuminating electron beam, and beam-induced sample damage limits the usable electron dose. The contrast can be increased by converting the electron beam's phase modulation into amplitude modulation using a phase plate, a device that applies a pi/2 radian phase shift to part of the electron beam after it has passed through the sample. Previous phase plate designs rely on material placed in or near the electron beam to provide this phase shift. This results in image aberrations, an inconsistent time-varying phase shift, and resolution loss when the electron beam charges, damages, or is scattered from the material.

In this seminar, I will present the theory, design, and implementation of the laser phase plate, which instead uses a focused continuous-wave laser beam to phase shift the electron beam. A near-concentric Fabry-Perot optical cavity focuses and resonantly enhances the power of the laser beam in order to achieve the high intensity required to provide the phase shift. We demonstrate that the cavity can surpass this requirement and generate a record-high continuous-wave laser intensity of 590 GW/cm^2. By integrating the cavity into a transmission electron microscope, we show that the ponderomotive potential of the laser beam applies a spatially selective phase shift to the electron beam. This enables us to make the first experimental observation of the relativistic reversal of the ponderomotive potential.

We then theoretically analyze the properties of the contrast transfer function generated by the laser phase plate. We experimentally determine that resolution loss caused by thermal magnetic field noise emanating from electrically conductive materials in the cavity can be eliminated by designing the cavity with a sufficiently large electron beam aperture. Finally, we show that the laser phase plate provides a stable pi/2 phase shift and concomitant contrast enhancement when imaging frozen hydrated biological macromolecules. We use these images to successfully determine the structure of the molecules. This demonstrates the laser phase plate as the first stable and lossless phase plate for transmission electron microscopy.

Please join us for this week’s AMO/QI seminar featuring Dr. Josh Combes, University of Colorado, Boulder. He will be giving a talk titled: Nonclassical light interacting with matter and nonclassical measurements 

Abstract: 

In this talk, I'll begin by summarizing a decade of research into the effects on matter interacting with non-classical light pulses, such as Schrödinger cat states or photon number states. These interactions generate notable correlations between the incoming and radiated light, inducing non-Markovian behavior in the matter. The latter part of the talk will focus on utilizing non-classical light for advancing precision metrology techniques. In particular, I will consider using a Schrödinger cat state as a local oscillator to develop novel measurements in optical and atomic interferometry.

Please join us for this week’s Spark talk featuring a presentation by Sam Gunn, who is a fourth-year Computer Science PhD student in the Theory Group at UC Berkeley. He will be speaking on the topic of: How to Use Quantum Indistinguishability Obfuscation.

Then join us after the talk on the patio for bagels as well as beverages and continued conversation.

Please join us for this week’s AMO/QI seminar featuring Dr. Nelson Oppong from JILA. Please note this seminar will take place on FRIDAY, March 22 from 1-2pm in 101 Campbell Hall. His talk is titled: Making, probing, and using 'Schrödinger cat' states in an optical clock

Abstract:
While optical atomic clocks continue to reach unprecedented levels of precision and accuracy, an important question concerns how quantum entanglement can be harnessed to improve their performance below the standard quantum limit. Our experiment combines techniques from atom arrays with the optical clock qubit of strontium to address this question. In this talk, I will discuss how we use laser-controlled Rydberg interactions to implement a multi-qubit gate for preparing 'Schrödinger cat' states on the clock qubit. We directly probe the performance of these Greenberger–Horne–Zeilinger type cat states in an atom-laser comparison and demonstrate performance below the standard quantum limit for short dark times. Using the programmability of our platform for the preparation of multiple atomic ensembles with variable sizes, we also explore a potential pathway toward Heisenberg-limited scaling of atomic clock precision.

Leonard Susskind from Stanford University presents a special lecture on How Quantum Complexity Found its Way into Black Hole Physics, as part of the Simons Institute’s workshop on Quantum Complexity: Quantum PCP, Area Laws, and Quantum Gravity. Come to Calvin Lab auditorium at the Simons Institute to learn more!

Abstract: Computational complexity is a very deep mathematical and logical concept that can give objective meaning to questions as varied as: How difficult is a theorem (some theorems are clearly more difficult than others); to how long a time does it take to produce a given quantum state of a quantum computer. But it has never till now been thought of as a physical property of a system. It was a great surprise that it found its way into black hole physics as a geometric property of black holes---the geometric size of their interiors. The introduction of complexity has greatly clarified the meaning of the black hole horizon. For example we now know that in many cases it is wrong to say that things cannot escape from behind the horizon; it is merely very complex. The horizon is also a censor that forbids an observer outside the black hole from witnessing violations of a profound physical principle: the so-called "quantum extended Church Turing Thesis." I'll try my best to explain these things.

Please join us for this week’s AMO/QI seminar featuring Dr. Sara Murciano, CalTech. She will be giving a talk titled: Measurements and symmetries on the fate of entanglement

Abstract:

 Entanglement plays a key role in different fields of physics. This talk focuses on two aspects where understanding its behaviour yields intriguing results: measurements and symmetries. The first topic explores how weak measurements alter the properties of critical models: We identify different protocols wherein measurements (i)  weakly modify the universal long-range entanglement and (ii) they completely obliterate it. As a potential practical application of this setup, I will show how it can be used to enable the teleportation of quantum states between distant parties and to what extent the entanglement of a many-body wavefunction transfers under imperfect teleportation protocols. The second subject concerns the study of the symmetry breaking in a subsystem. This investigation leads to the definition of the entanglement asymmetry, which neatly detects novel physical out-of-equilibrium features, in particular an unexpected quantum version of Mpemba effect.

Please join us for this week’s AMO/QI seminar featuring Dr. Nathanan Tantivasadakarn, CalTech. He will be giving a talk titled, Sculpting quantum many-body states and quantum error correcting codes with measurements.

Abstract:
Quantum mechanics exhibits a stark dichotomy between unitary time-evolution and measurement. These aspects are further contrasted by the fact that traditional many-body quantum theory is developed solely based on unitary aspects. In this talk, I will explore two fruitful synergies that emerge from the interplay between many-body quantum physics and the non-equilibrium quantum dynamics that arises from measurements. First, I will show how measurements can be used to circumvent fundamental constraints imposed by unitary dynamics and efficiently prepare a large class of topological phases of matter. In addition to discovering a new hierarchy of many-body quantum states unseen in the unitary setup and a surprising connection to the unsolvability of the quintic polynomial, our studies also yield practical protocols for quantum processors that led to the first unambiguous observation of non-Abelian anyons. Second, I will show how insights from topological phases of matter can in turn contribute to a physical understanding of the newly introduced "Floquet" quantum error correcting codes, featuring a schedule of anticommuting measurements. I will demonstrate that periodicity in time is in fact not required, unlocking a more general construction of "dynamic codes" that are capable of not just error correction, but also fault-tolerant quantum computation.

Please join us for this week’s Spark talk featuring a presentation by graduate student Sajant Anand from UC Berkeley. He will be speaking on the topic of: Quantum dynamics on a 127 Qubit Processor.

Then join us after the talk on the patio for boba and empanadas as well as beverages and continued conversation.

Please join us for this week’s AMO/QI seminar featuring Dr. Harry Levine from Amazon Web Services. He will be giving a talk titled: Novel strategies for hardware-efficient quantum processors

Abstract:
Quantum error correction is an exciting scientific frontier at the interface of many fields including quantum information science, many-body physics, and computer science. The field has developed rapidly in the last several years, with major milestones marking the first glimpses into a future of error-corrected quantum computers. At the same time, these advances have also illuminated the major science and engineering challenges that remain on the road to useful fault-tolerant quantum computers due to large resource overheads and demanding performance and control requirements. In this talk, I will discuss recent progress in strategies to ease the demands of error correction with a focus on two leading quantum information platforms: superconducting circuits and cold atoms. First, I will discuss the paradigm of “erasure qubits” which are qubits for which errors can be flagged in real-time and are consequently easier to correct. In this context, I will discuss recent experiments showing how erasure qubits can be realized using a “dual-rail” encoding in superconducting transmons, offering a way to package standard qubit components into better error correction building blocks. Second, I will discuss the recent, rapid progress in neutral atom quantum computers and highlight how the unique capabilities for efficient and flexible control can ease the path towards scalable operation of error-corrected quantum processors.

Please join us for this week’s Spark talk featuring a presentation by visiting assistant professor Zhiyan Ding. He will be speaking on the topic of: Single-ancilla ground state preparation via Lindbladians

Then join us after the talk on the patio for pizza and beverages and continued conversation.

Please join us for this week’s AMO/QI seminar featuring a talk by Dr. Sophia Economou from Virignia Tech.
Her talk is titled: Spin-photon interfaces: control and distribution of entanglement
Abstract:
Spin-photon interfaces are ubiquitous in quantum information processing and also feature intriguing physics culminating from the interplay of spin-spin, spin-photon, and spin-field interactions. In these systems, of particular interest are entangled states of nuclear spins, which can be used as quantum memories, and of photonic qubits, which can be used to transmit information robustly. I will discuss the dynamics of these systems and applications to quantum networks and photonic quantum computing.

Bio:
Sophia Economou is a Professor and the T. Marshall Hahn Chair in Physics at Virginia Tech. She is also the director of the Virginia Tech Center for Quantum Information Science and Engineering. She focuses on theoretical research in quantum information science, including quantum computing, quantum communications, and quantum simulation algorithms.

Please join us for this week’s Spark talk featuring a presentation by Prof. Shimon Kolkowitz from UC Berkeley. He will be speaking on the topic of: Erasure error conversion for quantum computing and quantum sensing

Then join us after the talk on the patio for mediterranean food as well as beverages and continued conversation.

Please join us for this week’s Spark talk featuring a presentation by PhD candidate Barak Nehoran from Princeton University. He will be speaking on the topic of: Unconditional Quantum Bit Commitments: from Impossibility to Possibility

Then join us after the talk on the patio for Freshroll and beverages and continued conversation.

Please join us for this week’s Spark talk featuring a presentation by Dr. Dan Borgnia from UC Berkeley. He will be speaking on the topic of: Quantized Adiabatic Pumping without Spectral Gaps

Then join us after the talk on the patio for burritos as well as beverages and continued conversation.

Please join us for this week’s AMO/QI seminar featuring Dr. Kenneth Brown from the Duke Quantum Center. He will give a talk titled: Simulating a conical intersection with a trapped ion quantum computer

Abstract:
Conical intersections often control the reaction products of photochemical processes and occur when two electronic potential energy surfaces intersect. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the ground potential energy surface, and although conical intersections have been observed experimentally, the geometric phase has not been directly observed in a molecular system. Here we use a trapped atomic ion system to perform a quantum simulation of a conical intersection. The ion’s internal state serves as the electronic state, and the motion of the atomic nuclei is encoded into the motion of the ions. The simulated electronic potential is constructed by applying state-dependent optical forces to the ion. We experimentally observe a clear manifestation of the geometric phase using adiabatic state preparation followed by motional state measurement. Our experiment shows the advantage of combining spin and motion degrees for quantum simulation of chemical reactions. We conclude with a discussion of future simulation directions. 

Please join us for this week’s Spark talk featuring a presentation by Prof. Hartmut Häeffner from UC Berkeley. He will be speaking on the topic of: What makes a good qubit?

Then join us after the talk on the patio for boba and empanadas as well as beverages and continued conversation.

The AMO Qual Club is meant for our early-career graduate students who are learning broadly about AMO physics in preparation for their qualifying examination.  This event is for graduate students, and in an effort to keep the gatherings more informal and less stressful, we ask professors, postdocs, undergraduate students, and other researchers not to join us for this meeting.

Please join us for a special CIQC Seminar featuring Dr. Aziza Suleymanzade (Harvard). She will give a talk titled: Quantum networking with solid-state defects in diamond nanophotonic cavities.

Abstract: Silicon-vacancy (SiV) defect centers in diamond coupled to nanophotonic crystal cavities offer a promising platform for quantum network applications. Our system utilizes long qubit coherence times, high optical cooperativity, and on-chip scalability, providing a unique path to the practical implementation of long-distance quantum networking. In this talk, I will present our recent results on generating long-distance distributed entanglement across a two-node network, demonstrating entanglement across a deployed 35-km telecom fiber network in the Boston/Cambridge area. I will also go over our ongoing projects, including the realization of blind delegated computing and applications for long-baseline entangled telescopes using our platform.

Please join us for this week’s AMO/QI seminar, on a special day, MONDAY Nov. 20 due to the Thanksgiving holiday.
Our speaker will be Dr. Lincoln Carr from the Colorado School of Mines. His talk is titled, Entangled quantum cellular automata, physical complexity, and Goldilocks rules

Abstract:
Cellular automata are interacting classical bits that display diverse emergent behaviors, from fractals to random-number generators to Turing-complete computation. We discover that quantum cellular automata (QCA) can exhibit complexity in the sense of the complexity science that describes biology, sociology, and economics. QCA exhibit complexity when evolving under 'Goldilocks rules' that we define by balancing activity and stasis. Our Goldilocks rules generate robust dynamical features (entangled breathers), network structure and dynamics consistent with complexity, and persistent entropy fluctuations. Present-day experimental platforms—Rydberg arrays, trapped ions, and superconducting qubits—can implement our Goldilocks protocols, making testable the link between complexity science and quantum computation exposed by our QCA.
The inability of classical computers to simulate large quantum systems is a hindrance to understanding the physics of QCA, but quantum computers offer an ideal simulation platform. I will discuss our recent experimental realization of QCA on a digital quantum processor, simulating a one-dimensional Goldilocks QCA rule on chains of up to 23 superconducting qubits. Employing low-overhead calibration and error mitigation techniques, we calculate population dynamics and complex network measures indicating the formation of small-world mutual information networks. Unlike random states, these networks decohere at fixed circuit depth independent of system size, the largest of which corresponds to 1,056 two-qubit gates.  This quantum circuit depth result presents a strong contrast to the quantum volume concept used to characterize many current quantum computers in industry. Such computations may open the door to the employment of QCA in applications like the simulation of strongly-correlated matter or beyond-classical computational demonstrations.

References:
1.     LE Hillberry, MT Jones, DL Vargas, P Rall, N Yunger Halpern, N Bao, S Notarnicola, S Montangero, LD Carr, “Entangled quantum cellular automata, physical complexity, and Goldilocks rules,” Quantum Science and Technology, v. 6, p. 045017 (2021)
2.     EB Jones, LE Hillberry, MT Jones, M Fasihi, P Roushan, Z Jiang, A Ho, C Neill, E Ostby, P Graf, E Kapit, and LD Carr, “Small-world complex network generation on a digital quantum processor,” Nature Communications v. 13, p. 4483 (2022)
3.     LE Hillberry, M Fasihi, L Piroli, N Yunger Halpern, T Prosen, and LD Carr, “Thermodynamics and integrability in quantum cellular automata,” Phys. Rev. Lett, to be submitted shortly (2023)