Spring 2026 Speakers
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February 4, 2026 - "Manipulating quantum systems by looking at them: Measurement-induced steering and cooling" by Yuval Gefen, Weizmann Institute of Science
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Abstract: Weak measurement is an alternative to von Neumann’s dogma of the “collapse” of a wavefunction: it avoids the necessity of the latter’s complete destruction, while capable of extracting partial information from the system measured. Concomitantly, measurement is associated with a back-action of the detector on the system’s state. This back-action can be harnessed for the purpose of steering a quantum state into a pre-designated target state, hence for quantum engineering of non-trivial states of matter. Likewise, one may employ this unavoidable backaction to extract energy from the system. I will try to package it all: steering, quantum cooling, and the relation to driving protocols of open systems and to active error correction platforms.
Abstract: Weak measurement is an alternative to von Neumann’s dogma of the “collapse” of a wavefunction: it avoids the necessity of the latter’s complete destruction, while capable of extracting partial information from the system measured. Concomitantly, measurement is associated with a back-action of the detector on the system’s state. This back-action can be harnessed for the purpose of steering a quantum state into a pre-designated target state, hence for quantum engineering of non-trivial states of matter. Likewise, one may employ this unavoidable backaction to extract energy from the system. I will try to package it all: steering, quantum cooling, and the relation to driving protocols of open systems and to active error correction platforms.
February 18, 2026 - "Bell nonlocality with arbitrary relaxation of Parameter and Measurement Independence" by Carlos Humberto, UNICAMP
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Abstract: Bell’s theorem establishes that no local hidden-variable model can reproduce all quantum
correlations. Such models are typically based on three key assumptions: measurement
independence (freedom of choice of measurement settings), parameter independence (no
influence of the distant choice of measurement), and outcome independence (no dependence
on the distant outcome, given the hidden variables). Loophole-free Bell experiments
show that at least one of these assumptions must fail in nature. A natural question,
however, is whether these assumptions might fail only partially—for instance, allowing
limited signaling, partial outcome dependence, or mild constraints on freedom of choice.
In this presentation, based on a recent work (https://www.nature.com/articles/s41467-025-59247-7), we will show that partial relaxations of measurement independence and parameter independence are still insufficient to reproduce quantum correlations. Specifically, we demonstrate that any hidden-variable theory that preserves outcome independence while allowing partial (yet arbitrarily close to complete) violations of measurement independence and parameter independence can be experimentally ruled out using many measurement settings on high-dimensional entangled states. Thus, if measurement independence or parameter independence fails, it must fail completely. These results significantly restrict the landscape of viable hidden-variable explanations of Bell nonlocality.
In this presentation, based on a recent work (https://www.nature.com/articles/s41467-025-59247-7), we will show that partial relaxations of measurement independence and parameter independence are still insufficient to reproduce quantum correlations. Specifically, we demonstrate that any hidden-variable theory that preserves outcome independence while allowing partial (yet arbitrarily close to complete) violations of measurement independence and parameter independence can be experimentally ruled out using many measurement settings on high-dimensional entangled states. Thus, if measurement independence or parameter independence fails, it must fail completely. These results significantly restrict the landscape of viable hidden-variable explanations of Bell nonlocality.
February 19, 2026 - "Are you lookin’ at me?” The observer effect in quantum tunneling and nonlinear optics by Aephraim Steinberg, University of Toronto
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ABSTRACT:
I will describe our ongoing experiments (and theory) looking into the nature of postselected quantum systems, using photons and cold atoms. I will focus on the following three questions:
• how long does a photon propagating through matter spend “trapped” as an atomic excitation, and is the answer different for transmitted and scattered photons?
• how should we think about a photon prepared with a definite energy, but later detected at a specific time? Can its effects on other systems share the advantages conferred by both of these incompatible properties?
• what happens to a particle when it is observed in a forbidden region? How rapid must such an observation be to collapse the state of the particle, thereby enhancing the transmission probability?
February 25, 2026 - "Bochner's theorem for finite inverse semigroups and its connection to Choi's theorem" by Sohail, Chapman University
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Abstract: Bochner's theorem characterizes positive definite functions on groups through the
positivity of their Fourier transforms and plays a fundamental role in Harmonic analysis.
While Bochner-type results are known for certain classes of semigroups, they typically
differ from the group theoretic formulations and do not retain the same level of simplicity
and generality.
This presentation is based on our recent work (https://arxiv.org/abs/2509.02529), in which we establish a Bochner-type theorem for finite inverse semigroups at the
level of matrix valued linear maps on the contracted algebras of the semigroups. Using
the intrinsic partial order of inverse semigroups, positivity naturally arises through
a Möbius-transformed map. Our main result characterizes the positive definiteness
of the Möbius transformed map in terms of the positivity of the Fourier transform
of the original map with respect to a complete family of inequivalent irreducible
representations of the contracted algebra induced by irreducible unitary representations
of the maximal subgroups of the inverse semigroup. The proof relies on Fourier inversion
formula, Schur orthogonality relations, and alternative characterizations of positive
definite maps, all established here in the setting of finite inverse semigroups. As
a special case, we show that for the inverse semigroup of matrix units, Bochner's
theorem reduces exactly to Choi's characterization of completely positive maps.
March 4, 2026 - "Majorization theory for quasiprobabilities" by Twesh Upadhyaya, University of Maryland
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Abstract: Majorization theory is a powerful mathematical tool to compare the disorder in distributions, with wide-ranging applications in many fields including mathematics, physics, information theory, and economics. While majorization theory typically focuses on probability distributions, quasiprobability distributions provide a pivotal framework for advancing our understanding of quantum mechanics, quantum information, and signal processing. Here, we introduce a notion of majorization for continuous quasiprobability distributions over infinite measure spaces. Generalizing a seminal theorem by Hardy, Littlewood, and Pólya, we prove the equivalence of four definitions for both majorization and relative majorization in this setting. We give several applications of our results in the context of quantum resource theories, obtaining new families of resource monotones and no-goes for quantum state conversions. A prominent example we explore is the Wigner function in quantum optics. More generally, our results provide an extensive majorization framework for assessing the disorder of integrable functions over infinite measure spaces.
Abstract: Majorization theory is a powerful mathematical tool to compare the disorder in distributions, with wide-ranging applications in many fields including mathematics, physics, information theory, and economics. While majorization theory typically focuses on probability distributions, quasiprobability distributions provide a pivotal framework for advancing our understanding of quantum mechanics, quantum information, and signal processing. Here, we introduce a notion of majorization for continuous quasiprobability distributions over infinite measure spaces. Generalizing a seminal theorem by Hardy, Littlewood, and Pólya, we prove the equivalence of four definitions for both majorization and relative majorization in this setting. We give several applications of our results in the context of quantum resource theories, obtaining new families of resource monotones and no-goes for quantum state conversions. A prominent example we explore is the Wigner function in quantum optics. More generally, our results provide an extensive majorization framework for assessing the disorder of integrable functions over infinite measure spaces.
April 1, 2026 - "Quantum Path Interference: A Bridge Between Quantum Optics and Strong-Field Ionization" by André Staudte, University of Ottawa
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Abstract: Quantum path-interference provides a common thread between quantum optics and photoionization. I will present an example of correlations in photoelectron momenta which constitute a direct entanglement witness, conceptually similar to signal-idler pairs in spontaneous parametric down-conversion.
Even single photoelectrons exhibit quantum path interference when diffracting from their parent molecule, yielding a static photoelectron hologram that encodes molecular geometry. Replacing the X-ray with a few-cycle mid-IR pulse adds an attosecond clock: rescattering converts the hologram into a time-resolved probe of tunnelling and transient structure in the strong-field regime.
Simultaneously, strong fields also produce interferometers for nuclear wavepackets: femtosecond pulses temporarily reshape the Born–Oppenheimer surfaces of H_2^+, splitting a nuclear wavepacket that later recombines; interference appears as delay-dependent modulation in proton momenta.
Taken together, these studies show how interferometric techniques can follow and steer the quantum motion of electrons and nuclei in intense laser fields, pointing toward controlled photochemistry and state-resolved molecular imaging.
Abstract: Quantum path-interference provides a common thread between quantum optics and photoionization. I will present an example of correlations in photoelectron momenta which constitute a direct entanglement witness, conceptually similar to signal-idler pairs in spontaneous parametric down-conversion.
Even single photoelectrons exhibit quantum path interference when diffracting from their parent molecule, yielding a static photoelectron hologram that encodes molecular geometry. Replacing the X-ray with a few-cycle mid-IR pulse adds an attosecond clock: rescattering converts the hologram into a time-resolved probe of tunnelling and transient structure in the strong-field regime.
Simultaneously, strong fields also produce interferometers for nuclear wavepackets: femtosecond pulses temporarily reshape the Born–Oppenheimer surfaces of H_2^+, splitting a nuclear wavepacket that later recombines; interference appears as delay-dependent modulation in proton momenta.
Taken together, these studies show how interferometric techniques can follow and steer the quantum motion of electrons and nuclei in intense laser fields, pointing toward controlled photochemistry and state-resolved molecular imaging.
Bio:
André Staudte is a Senior Research Officer at the National Research Council of Canada
and an Adjunct Professor at the University of Ottawa, where he co-directs the Joint
Centre for Extreme Photonics. He leads an experimental program in attosecond and strong-field
physics, with a focus on imaging and controlling electron and nuclear dynamics in
atoms, molecules, and solids using ultrafast laser fields. His work spans photoelectron
spectroscopy, high-harmonic generation, and emerging directions in attosecond quantum
optics, including the use of nonclassical light. Staudte has contributed to the development
of advanced instrumentation such as COLTRIMS-based techniques and their extensions,
enabling time-resolved studies of quantum motion on its natural timescales.
April 8, 2026 -" If you can’t tell you’re in a superposition, then your dynamics is linear (and vice-versa)" by Jacques Pienaar, University of Chicago
Abstract: I consider a generalized version of Galileo's famous "ship" argument: a
scientist sealed inside the hold of a ship cannot tell by any experiment whether or
not the whole ship is in a definite macroscopic state, or a coherent quantum (or general-probabilistic)
"superposition" of such states, as judged by someone observing from the outside. I
prove that if we elevate this to a general postulate within a general probabilistic
setting, then dynamics must be (convex-)linear. Conversely, if dynamics were non-linear,
someone sealed within the "ship" could do an experiment to determine that the whole
ship is in a superposition.
April 15, 2026 - "Interpretations of probability: philosophical and historical reflections" by Wayne Myrvold , Western University
Abstract: The use of probability, in physics and other areas of science, raises the
question: what are we saying, when we make a probability ascription? This is a question
to which a number of divergent answers have been given. In this talk I will address
this issue, with reference to the discussions that went on in the 19th century, as our modern theory of probability was being developed. This will include
discussions of why writers such as Poisson and Cournot came to distinguish between
two notions of probability (this is the distinction that, in current philosophical
usage, between "chance" and credence".) It will also review discussions in the 19th century of what has come to be called (following Keynes) the Principle of Indifference,
and why (contrary to a common view) it was never a widely accepted principle. All
of this will have relevance for how we should think of uses of probability in current
physics.
April 22, 2026 - "Causal decompositions of unitary transformations" by Tein van der Lugt , Perimeter Institute
Abstract: If a multipartite unitary transformation admits of a circuit representation
that has no path from input A to output B, then system B does not causally depend
on system A through the overall unitary transformation. I will talk about the converse:
if a unitary satisfies a given set of causal independence conditions between its inputs
and outputs, then is there a circuit decomposition of the unitary that represents
those conditions in terms of absences of paths? Answering this question constitutes
the research programme of ‘causal decompositions’, and turns out to be pretty tricky
in general. Concrete applications lie in the field of quantum foundations and quantum
causality, where causal structure and compositional structure often tend to be conflated.
I will present some progress on the question that uses tools from lattice theory (and
I will explain physically why it is that these lattices show up naturally).
April 29,2026 - " A Brief History of the Rainbow Effect" by Marko Cosic, Chapman University
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Abstract: In this lecture, we shall follow the historical development of human fascination with the rainbow effect, which has arguably occupied the human imagination since the dawn of time. Since the evolution of understanding of the rainbow effect spanned at least several thousand years, it is impossible to present a complete portrait in one lecture. Instead, we shall focus on the evolution of key ideas that led scientists to abandon supernatural explanations in favor of explanations based on rational principles, culminating in the current model of the rainbow effect, proposed by M. Nussenzveig and experimentally verified at the University of Rochester in the 1970s.
Abstract: In this lecture, we shall follow the historical development of human fascination with the rainbow effect, which has arguably occupied the human imagination since the dawn of time. Since the evolution of understanding of the rainbow effect spanned at least several thousand years, it is impossible to present a complete portrait in one lecture. Instead, we shall focus on the evolution of key ideas that led scientists to abandon supernatural explanations in favor of explanations based on rational principles, culminating in the current model of the rainbow effect, proposed by M. Nussenzveig and experimentally verified at the University of Rochester in the 1970s.
What is fascinating in this story is that progress is not continuous. For example,
approaches based on geometrical optics, which were incrementally developed over a
long period and successfully explained certain aspects of the rainbow effect, failed
catastrophically to explain others. To progress further, it was necessary to completely
abandon the concept of the corpuscular nature of light in favor of the wave theory
of light, which provided an analytical solution to the problem.
As in any good story, this one has multiple plot twists. It has turned out that the
analytical solution was practically useless, as it was given by an infinite sum of
rapidly oscillating terms depending on multiple parameters, making the sum converge
extremely slowly to the correct value. In the age before computers, even evaluating
the exact solution was a very difficult, if not futile, endeavor.
Nowadays, we have efficient computer algorithms that enable accurate evaluation of
the analytical solution. However, the drawback now is that the multiple-parameter
physics of the rainbow effect is buried deep within the generated numbers, and there
is no simple way to extract it. Again, the formulation of a qualitatively and quantitatively
correct model required a new set of ideas, borrowed this time from concepts in quantum
mechanics.
In the end, we shall briefly review other recent observations of the rainbow scattering
effect and argue that we will probably never achieve a complete understanding of the
rainbow effect as long as scientists, intrigued by its beauty and apparent simplicity,
continue to ask new questions.
Fall 2025 Speakers:
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August 11, 2025 - "Living-State Physics: How Thermodynamics begets Biology" by Avshalom Elitzur, Chapman University
August 11, 2025 - "Why Have We Been Wrong About Quantum Theory for So Long?" by Yakir Aharonov, Chapman University
September 3, 2025 - "A finite-resources description of a measurement process and its implications for the" Wigner's Friend" scenario" by Fernando de Melo, Centro Brasileiro de Pesquisas Físicas - CBPF
Abstract: Quantum mechanics now informs technologies like large-scale quantum computers, making foundational issues technologically relevant. In this seminar, I will present a model of quantum measurement that incorporates finite-resource constraints for macroscopic systems. In this framework, collapse emerges as an effective description of closed dynamics. Applying it to Wigner’s Friend, we find that both observers agree once Wigner adopts the finite-resources view.
September 10, 2025 - "No-local-broadcasting theorem for non-signalling behaviours and assemblages" by Carlos Vieira, UNICAMP
Abstract: The no-broadcasting theorem is a cornerstone of quantum information theory, showing
that quantum states cannot be copied. A natural question is whether this limitation
is uniquely quantum, or if it also applies more broadly to non-classical theories.
In this talk, I will discuss a generalisation to the framework of non-signalling behaviours,
and show that nonlocal behaviours cannot be locally broadcast. The proof relies on
fundamental properties of the relative entropy for behaviours, and a similar line
of reasoning also establishes an analogous no-broadcasting result for steerable assemblages.
September 17 , 2025 - "What do black holes teach us about Wigner's Friend?" by Emily Adlam, Chapman University
Abstract: Recently, Hausman and Renner have pointed out that several famous paradoxes relating to black holes have a similar character to various Extended Wigner's Friend paradoxes. Given these connections, studying the black hole paradoxes may offer an interesting way to get some new insight into the Wigner's Friend paradoxes. In this talk I will introduce the four paradoxes described by Hausman and Renner, then note some important similarities and differences between them and make some suggestions about what these connections might tell us about the original Wigner's Friend paradoxes. In particular, I argue that the black hole comparison may push us toward intrinsic relationality and toward some kind of retrocausal or atemporal solution.
September 24, 2025 - " Divide-and-Conquer Simulation of Open Quantum Systems" by Nadja Bernardes,Universidade Federal de Pernambuco
Abstract: One of the promises of quantum computing is to simulate physical systems efficiently. However, the simulation of open quantum systems - where interactions with the environment play a crucial role - remains challenging for quantum computing, as it is impossible to implement deterministically non-unitary operators on a quantum computer without auxiliary qubits. The Stinespring dilation can simulate an open dynamic but requires a high circuit depth, which is impractical for NISQ devices. An alternative approach is parallel probabilistic block-encoding methods, such as the Sz.-Nagy and Singular Value Decomposition dilations. These methods result in shallower circuits but are hybrid methods, and we do not simulate the quantum dynamic on the quantum computer. In this work, we describe a divide-and-conquer strategy for preparing mixed states to combine the output of each Kraus operator dilation and obtain the complete dynamic on quantum hardware with a lower circuit depth. The work also introduces a balanced strategy that groups the original Kraus operators into an expanded operator, leading to a trade-off between circuit depth, CNOT count, and number of qubits. We perform a computational analysis to demonstrate the advantages of the new method and present a proof-of-concept simulation of the Fenna-Matthews-Olson dynamic on current quantum hardware.
October 1, 2025 - "Certification of entangled measurements--A moment matrix approach" by Ranieri Nery , Institute of Photonic Sciences (ICFO)
Abstract: "The ability to identify and certify non-classical properties in networks with uncharacterized
devices is nowadays an essential tool for enabling applications that exploit quantum
advantages over classical resources in a device-independent manner. It is also crucial
for advancing our understanding of the foundations of quantum theory. Much attention
has been devoted to certifying entangled states as sources of correlations, and comprehensive
tests for this task have been developed in the literature. By contrast, their counterpart—entangled
measurements—has received only limited attention, despite being a fundamental resource
in applications such as teleportation and entanglement swapping.
In this work, we contribute to methods tailored for probing measurements by adapting a technique based on moment matrices—fundamental objects in the theory of polynomial optimization over non-commutative variables, originally introduced in the Navascués–Pironio–Acín (NPA) hierarchy [1], essential for approximating quantum-achievable probabilities. We demonstrate its utility in a test case where a Bell-state measurement is applied to two independent, maximally entangled bipartite states in a network of three separated observers. The test builds on a variant of the NPA hierarchy introduced by Moroder et al. [2], which enables separability tests of quantum states in device-independent settings. We present and analyze our results, discuss a possible duality between our test and tests on corresponding induced states, and explore extensions to modified networks that may yield further refinements of the technique
In this work, we contribute to methods tailored for probing measurements by adapting a technique based on moment matrices—fundamental objects in the theory of polynomial optimization over non-commutative variables, originally introduced in the Navascués–Pironio–Acín (NPA) hierarchy [1], essential for approximating quantum-achievable probabilities. We demonstrate its utility in a test case where a Bell-state measurement is applied to two independent, maximally entangled bipartite states in a network of three separated observers. The test builds on a variant of the NPA hierarchy introduced by Moroder et al. [2], which enables separability tests of quantum states in device-independent settings. We present and analyze our results, discuss a possible duality between our test and tests on corresponding induced states, and explore extensions to modified networks that may yield further refinements of the technique
October 8, 2025 - "CDJ-Pontryagin Optimal Control for General Continuously Monitored Quantum Systems" by Tathagata Karmakar, University of California, Berkely
Abstract: The Chantasri-Dressel-Jordan (CDJ) stochastic path integral formalism (Chantasri et al. 2013 and 2015) characterizes the statistics of the readouts and the most likely conditional evolution of a continuously monitored quantum system. Recent explorations suggest the most likely paths can help find optimal control protocols in monitored quantum systems. However, such an approach has only been applied to a selected few cases, and a systematic investigation into the CDJ formalism for arbitrary quantum systems was lacking. In my talk, I will show how to generalize the CDJ formalism’s most likely paths by introducing a costate operator. Then, the most likely path can be cast as a quantum Pontryagin's maximum principle, where the cost function is the readout probabilities along a quantum trajectory. This insight allows us to derive a general optimal control framework for quantum systems undergoing arbitrary dynamics. As an example, we analyze a monitored oscillator in the presence of a parametric quadratic potential and variable quadrature measurements. In this case, the optimal parametric potential is analytically shown to have a “bang-bang” form. We apply our protocol to three quantum oscillator state preparation problems relevant to Bosonic quantum computing. The optimal controls from the CDJ-Pontryagin approach show a 40-196% increase in the number of trajectories reaching more than 95% fidelities, compared to non-optimal controls. If time permits, I will also delve into optimal control protocols for solving classical optimization problems such as k-SAT.
October 15 , 2025 - "Free snacks in quantum complexity" by Gerard McCaul, Tulane University
Abstract: Estimating ground-state energies is a cornerstone problem in Hamiltonian complexity.
There is however no such thing as a free lunch, and in general solving this problem
requires exponential resources even on quantum computers. It is in this context we
analyse the recently developed Imaginary-Time Quantum Dynamical Emulation (ITQDE).
This method enables estimation of spectral densities, partition functions, and low-lying
gaps, but requires only minimal coherent control, modest classical post-processing,
and no particular state preparation. Using a quadrature-based formulation, we derive
scaling and stability criteria that diagnose when its estimates are reliable, and
introduce a controlled smoothing that yields a principled bias-variance trade off.
The resulting picture preserves the hardness of exact eigenvalue resolution but reveals
a practical regime - a "free snack" - where coarse-grained spectral information is
obtainable with only polynomial resources. By recasting sampling costs as explicit
bounds on resolvable bandwidths, the intermediate regime between trivial and intractable
complexity becomes a tunable target potentially accessible on near-term quantum hardware.
October 22, 2025 - IQS Public Talk “Resilience of a quantum physicist inside the Ukraine - Russian war” by Dr. Gleb Skorobagatko
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Abstract: Resilience.. Resilience to be curious, resilience to think, to create, to live your life your way. These are the necessary conditions for a human being not only to live a life profoundly, but also these are necessary conditions for one to act in science effectively, to be a scientist.. But, sometimes, life delivers you special challenges, which try your ability to follow your way. The wartime is, obviously, such a case. The war in Ukraine, which continues for more than 3,5 years already, has filled the above simple statements with a very special meaning for every scientist living inside the country during all that time. This talk is an attempt to share with the audience the most important aspects of my individual wartime experience in the framework of my previous professional scientific path. What kind of challenges does a scientist face in the country at war? How to continue your individual professional path under such circumstances? Where to get energy, optimism and creativity from (spoiler: that's probably one's hardest task during the wartime) when you are in the country at war ? What can help one to be resilient, to continue one's scientific way despite all the critical obstacles, doubts and uncertainties ? - In my talk I shall try to answer these questions from my own experience of living for 3,5 years in wartime Ukraine.
October 29, 2025 - "Unifying quantum Zeno and anti-Zeno effects" by Sacha Greenfield, University of Southern California
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Abstract: The quantum Zeno effect is a striking feature of quantum mechanics with foundational implications and practical applications in quantum control, error suppression, and error correction. It has branched off into a variety of different interpretations, making it easy to miss the unifying features of the underlying effect. In particular, the quantum Zeno effect has been studied in the context of both selective and nonselective measurements; for both pulsed and continuous interactions; for suppression and enhancement of decay (Zeno / anti-Zeno effects); and even in the absence of measurement entirely. In this talk, I’ll discuss our recent work examining how all these effects arise in the context of a driven qubit subjected to measurements or dissipation. Zeno and anti-Zeno effects are revealed as regimes of a unified effect that appears whenever a measurement-like process competes with a non-commuting evolution.
Abstract: The quantum Zeno effect is a striking feature of quantum mechanics with foundational implications and practical applications in quantum control, error suppression, and error correction. It has branched off into a variety of different interpretations, making it easy to miss the unifying features of the underlying effect. In particular, the quantum Zeno effect has been studied in the context of both selective and nonselective measurements; for both pulsed and continuous interactions; for suppression and enhancement of decay (Zeno / anti-Zeno effects); and even in the absence of measurement entirely. In this talk, I’ll discuss our recent work examining how all these effects arise in the context of a driven qubit subjected to measurements or dissipation. Zeno and anti-Zeno effects are revealed as regimes of a unified effect that appears whenever a measurement-like process competes with a non-commuting evolution.
October 30, 2025 - "Scale-efficient quantum error correction using concatenated bosonic qubits" by Fernando Brandao, CalTech
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Abstract: In order to solve problems of practical importance, quantum computers will likely require error correction which encodes fault-tolerant logical qubits into many noisy physical qubits. The large overheads projected for achieving fault-tolerant quantum computers motivate the search for more hardware-efficient platforms error-correction strategies. A promising direction to reduce the error correction overhead is to employ bosonic qubits, formed by states of a bosonic mode. I will discuss an experimental realization of a logical qubit at the AWS Center for Quantum Computing. We built a superconducting circuit which implements a repetition code up to distance five of cat qubits stabilized in bosonic modes. Phase-flip errors on the data cat qubits are corrected by the repetition code using ancilla transmons. The cat qubits are passively protected against bit-flip errors by two photon dissipation and all the operations needed for error correction, including the controlled-not gate, retain a bias against bit-flip errors. Our experiment is the first to leverage built-in bosonic error correction in concert with an outer concatenated code and biased noise.
Abstract: In order to solve problems of practical importance, quantum computers will likely require error correction which encodes fault-tolerant logical qubits into many noisy physical qubits. The large overheads projected for achieving fault-tolerant quantum computers motivate the search for more hardware-efficient platforms error-correction strategies. A promising direction to reduce the error correction overhead is to employ bosonic qubits, formed by states of a bosonic mode. I will discuss an experimental realization of a logical qubit at the AWS Center for Quantum Computing. We built a superconducting circuit which implements a repetition code up to distance five of cat qubits stabilized in bosonic modes. Phase-flip errors on the data cat qubits are corrected by the repetition code using ancilla transmons. The cat qubits are passively protected against bit-flip errors by two photon dissipation and all the operations needed for error correction, including the controlled-not gate, retain a bias against bit-flip errors. Our experiment is the first to leverage built-in bosonic error correction in concert with an outer concatenated code and biased noise.
November 11, 2025 - IQS Public Talk: "Understanding the 2025 Nobel Prize in Physics" by Justin Dressel
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Abstract: Quantum mechanics was developed to describe the very small: atoms, subatomic structure, and fundamental particles. How big can things become while still showing fundamentally quantum behavior? This year's Nobel Prize was awarded to three researchers who had the audacity to show that macroscopic collections of charges moving in a supercooled electronic circuit can still behave quantum mechanically, allowing us to engineer macroscopic artificial atoms: John Clarke, John Martinis, and Michel Devoret. This talk will tell their story, what they showed, and how their demonstration has now become one of the cornerstones of modern superconducting quantum computation.
Abstract: Quantum mechanics was developed to describe the very small: atoms, subatomic structure, and fundamental particles. How big can things become while still showing fundamentally quantum behavior? This year's Nobel Prize was awarded to three researchers who had the audacity to show that macroscopic collections of charges moving in a supercooled electronic circuit can still behave quantum mechanically, allowing us to engineer macroscopic artificial atoms: John Clarke, John Martinis, and Michel Devoret. This talk will tell their story, what they showed, and how their demonstration has now become one of the cornerstones of modern superconducting quantum computation.
November 12, 2025 - “Non-Hermitian Evolution from Continuous Monitoring” by Justin Dressel
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Abstract:In modern superconducting processors, it is possible to continuously monitor information about a quantum bit while it is evolving. A traveling microwave field briefly interacts with the qubit then is later measured, yielding a signal that is generally correlated with the qubit and thus partially collapses the qubit state. The resulting conditioned evolution of the reduced qubit state exhibits competition between unitary and collapse dynamics, so is fundamentally non-Hermitian and stochastic in character. Moreover, the specific character of the dynamics can often be resolved long after the qubit interacts with the traveling field, yielding a dynamical version of a delayed choice paradox. This talk clarifies how these conditioned dynamics correspond to a pre- and post-selected time-dependent Hamiltonian that involves complex weak values of observables interacting with the qubit. The complex and delayed-choice nature of the effective qubit Hamiltonian is determined by the boundary conditions connecting the prepared input field to the amplified and observed output signal.
Abstract:In modern superconducting processors, it is possible to continuously monitor information about a quantum bit while it is evolving. A traveling microwave field briefly interacts with the qubit then is later measured, yielding a signal that is generally correlated with the qubit and thus partially collapses the qubit state. The resulting conditioned evolution of the reduced qubit state exhibits competition between unitary and collapse dynamics, so is fundamentally non-Hermitian and stochastic in character. Moreover, the specific character of the dynamics can often be resolved long after the qubit interacts with the traveling field, yielding a dynamical version of a delayed choice paradox. This talk clarifies how these conditioned dynamics correspond to a pre- and post-selected time-dependent Hamiltonian that involves complex weak values of observables interacting with the qubit. The complex and delayed-choice nature of the effective qubit Hamiltonian is determined by the boundary conditions connecting the prepared input field to the amplified and observed output signal.
