January 2025 - ITP-quantumseminare

Monday's QIT seminar at 16:00 in HIT E 41.1
by Ladina Hausmann 03 Feb '25

03 Feb '25

Hi all, next Monday Kai Ott will present his master thesis at IBM entitled “Decision-tree decoders for general quantum LDPC codes”. The talk will take place at 16:00 in HIT E41.1 and on zoom https://ethz.zoom.us/j/362994444, see below for the abstract. Best, Ladina **** Title: Decision-tree decoders for general quantum LDPC codes Abstract: As diverse approaches to fault-tolerant quantum computing rapidly evolve, flexible decoders for a wide range of settings are becoming increasingly desirable. We introduce Decision Tree Decoders (DTDs), a new class of decoding algorithms for general quantum low-density parity-check (qLDPC) codes that require only sparsity of the binary check matrix. DTDs construct corrections incrementally by adding faults one-by-one, forming a path through a Decision Tree (DT). Each DTD algorithm is defined by its strategy for exploring the tree, with well-designed algorithms typically needing to explore only a small portion before finding a correction. We propose two explicit DTD algorithms for general qLDPC codes: (1) A provable decoder: Guaranteed to find a minimum-weight correction. While it can be slow in the worst case, numerical results show surprisingly fast median-case runtime, exploring only w DT nodes to find a correction for weight-w errors in notable qLDPC codes, such as bivariate bicycle and color codes. This decoder may be valuable for ensemble decoding and determining provable code distances. The tools underpinning this decoder can also be repurposed to compute all minimum-weight logical operators of a code. (2) A heuristic decoder: Achieves higher accuracy and faster performance than BP-OSD on the gross code with circuit noise in realistic parameter regimes.

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Monday's QIT seminar at 15:00
by Ladina Hausmann 25 Jan '25

25 Jan '25

Hi all, on Monday Ali Akil will talk about “Quantum Superposition Of Black Hole Evaporations”. The talk will take place at 15:00 in HIT J 52. See below for the abstract. Best, Ladina ****** Title: Quantum Superposition Of Black Hole Evaporations Abstract: We revisit Hawking’s black hole evaporation process, allowing a quantum superposition of black hole masses. The Hawking particles created inside the black hole are assumed to annihilate with the black hole matter. Since the Hawking particles have an undetermined energy, the black hole evolves into a superposition of being fully evaporated and not fully evaporated. In the branches of the superposition where the matter is fully evaporated, the outgoing Hawking particles encode the initial state of the black hole matter. In the branches where the black hole is not fully evaporated, more Hawking particle pairs continue to be created. We model this branch-dependent pair creation with controlled unitaries, which take into account the back-reaction of the radiation emission on the black hole state. With every burst of radiation the probability of the full annihilation strictly increases, until the black hole is (asymptotically) fully evaporated in every branch of the quantum superposition. In this model the evaporation is unitary and the initial state can in principle be recovered from the radiation.

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Next week's QIT seminars
by Ladina Hausmann 17 Jan '25

17 Jan '25

Hi all, next week there are two talks scheduled: 1. On Monday Finn Holler will tell us about “Quantum key distribution with less randomness”. The talk will take place at 16:00 in HIT E41.1 2. On Wednesday Renata Ferrero will tell us about “Observables and observers in quantum spacetime: a field theory perspective”. The talk will take place at 11:00 in HIT K51. See below for the abstracts. Best, Ladina ********** Title: Quantum key distribution with less randomness Abstract: Perfect randomness is a key resource in cryptographic protocols, including quantum key distribution (QKD). Security proofs often rely on the availability of uniform and independent random bits, which are hard to obtain in practice. For instance, in QKD, the two honest parties Alice and Bob, typically use a uniformly random subset of rounds for statistical analysis during parameter estimation. By a random sampling argument, these observations are then used to make inferences about the remaining rounds. We investigate the use of samplers in parameter estimation, in order to reduced the randomness consumption of the protocol. Secondly, we investigated how a security proof would need to be adapted when a truly random source is replaced by a semi-random one, described by the Santha-Vazirani model. *** Title: Observables and observers in quantum spacetime: a field theory perspective Abstract: Geometrical information of the quantum spacetime which we try to observe is carried by physical fields. Hence, observables cannot be properties of the “quantum spacetime” alone, but must also depend on the experimental setup that is used in order to probe them. I will give an overview about how to construct relational observables in both the canonical and the covariant (field theory) formalism and discuss their differences. I will then focus on the inclusion of quantum reference frames within the renormalization group program in quantum field theory.

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No seminar next week
by Ladina Hausmann 04 Jan '25

04 Jan '25

Hi all, Happy new year! Next week and the week after that no seminar planned, the next planned talk is on the 20th of January by Finn Holler. Best, Ladina

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