11 research outputs found
A computationally universal phase of quantum matter
We provide the first example of a symmetry protected quantum phase that has
universal computational power. Throughout this phase, which lives in spatial
dimension two, the ground state is a universal resource for measurement based
quantum computation.Comment: 5 + 2 page
Optimizing Quantum Error Correction Codes with Reinforcement Learning
Quantum error correction is widely thought to be the key to fault-tolerant
quantum computation. However, determining the most suited encoding for unknown
error channels or specific laboratory setups is highly challenging. Here, we
present a reinforcement learning framework for optimizing and fault-tolerantly
adapting quantum error correction codes. We consider a reinforcement learning
agent tasked with modifying a family of surface code quantum memories until a
desired logical error rate is reached. Using efficient simulations with about
70 data qubits with arbitrary connectivity, we demonstrate that such a
reinforcement learning agent can determine near-optimal solutions, in terms of
the number of data qubits, for various error models of interest. Moreover, we
show that agents trained on one setting are able to successfully transfer their
experience to different settings. This ability for transfer learning showcases
the inherent strengths of reinforcement learning and the applicability of our
approach for optimization from off-line simulations to on-line laboratory
settings.Comment: 21 pages, 13 figures, 1 table, updated reference list, accepted for
publication in Quantu
Automated Gadget Discovery in Science
In recent years, reinforcement learning (RL) has become increasingly
successful in its application to science and the process of scientific
discovery in general. However, while RL algorithms learn to solve increasingly
complex problems, interpreting the solutions they provide becomes ever more
challenging. In this work, we gain insights into an RL agent's learned behavior
through a post-hoc analysis based on sequence mining and clustering.
Specifically, frequent and compact subroutines, used by the agent to solve a
given task, are distilled as gadgets and then grouped by various metrics. This
process of gadget discovery develops in three stages: First, we use an RL agent
to generate data, then, we employ a mining algorithm to extract gadgets and
finally, the obtained gadgets are grouped by a density-based clustering
algorithm. We demonstrate our method by applying it to two quantum-inspired RL
environments. First, we consider simulated quantum optics experiments for the
design of high-dimensional multipartite entangled states where the algorithm
finds gadgets that correspond to modern interferometer setups. Second, we
consider a circuit-based quantum computing environment where the algorithm
discovers various gadgets for quantum information processing, such as quantum
teleportation. This approach for analyzing the policy of a learned agent is
agent and environment agnostic and can yield interesting insights into any
agent's policy
Operationally meaningful representations of physical systems in neural networks
To make progress in science, we often build abstract representations of
physical systems that meaningfully encode information about the systems. The
representations learnt by most current machine learning techniques reflect
statistical structure present in the training data; however, these methods do
not allow us to specify explicit and operationally meaningful requirements on
the representation. Here, we present a neural network architecture based on the
notion that agents dealing with different aspects of a physical system should
be able to communicate relevant information as efficiently as possible to one
another. This produces representations that separate different parameters which
are useful for making statements about the physical system in different
experimental settings. We present examples involving both classical and quantum
physics. For instance, our architecture finds a compact representation of an
arbitrary two-qubit system that separates local parameters from parameters
describing quantum correlations. We further show that this method can be
combined with reinforcement learning to enable representation learning within
interactive scenarios where agents need to explore experimental settings to
identify relevant variables.Comment: 24 pages, 13 figure
Symmetry-enriched topological order from partially gauging symmetry-protected topologically ordered states assisted by measurements
Symmetry protected topological phases exhibit nontrivial short-ranged
entanglement protected by symmetry and cannot be adiabatically connected to
trivial product states while preserving the symmetry. In contrast, intrinsic
topological phases do not need ordinary symmetry to stabilize them and their
ground states exhibit long-range entanglement. It is known that for a given
symmetry group , the 2D SPT phase protected by is dual to the 2D
topological phase exemplified by the twisted quantum double model
via gauging the global symmetry . Recently it was realized
that such a general gauging map can be implemented by some local unitaries and
local measurements when is a finite, solvable group. Here, we review the
general approach to gauging a -SPT starting from a fixed-point ground-state
wave function and applying a -step gauging procedure. We provide an in-depth
analysis of the intermediate states emerging during the N-step gauging and
provide tools to measure and identify the emerging symmetry-enriched
topological order of these states. We construct the generic lattice parent
Hamiltonians for these intermediate states, and show that they form an
entangled superposition of a twisted quantum double with an SPT ordered state.
Notably, we show that they can be connected to the TQD through a finite-depth,
local quantum circuit which does not respect the global symmetry of the SET
order. We introduce the so-called symmetry branch line operators and show that
they can be used to extract the symmetry fractionalization classes and symmetry
defectification classes of the SET phases with the input data and
of the pre-gauged SPT ordered state. We illustrate
the procedure of preparing and characterizing the emerging SET ordered states
for some Abelian and non-Abelian examples such as dihedral groups and the
quaternion group .Comment: 26+21 pages, 18+4 figure
Automated gadget discovery in the quantum domain
In recent years, reinforcement learning (RL) has become increasingly successful in its application to the quantum domain and the process of scientific discovery in general. However, while RL algorithms learn to solve increasingly complex problems, interpreting the solutions they provide becomes ever more challenging. In this work, we gain insights into an RL agent’s learned behavior through a post-hoc analysis based on sequence mining and clustering. Specifically, frequent and compact subroutines, used by the agent to solve a given task, are distilled as gadgets and then grouped by various metrics. This process of gadget discovery develops in three stages: First, we use an RL agent to generate data, then, we employ a mining algorithm to extract gadgets and finally, the obtained gadgets are grouped by a density-based clustering algorithm. We demonstrate our method by applying it to two quantum-inspired RL environments. First, we consider simulated quantum optics experiments for the design of high-dimensional multipartite entangled states where the algorithm finds gadgets that correspond to modern interferometer setups. Second, we consider a circuit-based quantum computing environment where the algorithm discovers various gadgets for quantum information processing, such as quantum teleportation. This approach for analyzing the policy of a learned agent is agent and environment agnostic and can yield interesting insights into any agent’s policy
Operationally meaningful representations of physical systems in neural networks
To make progress in science, we often build abstract representations of physical systems that meaningfully encode information about the systems. Such representations ignore redundant features and treat parameters such as velocity and position separately because they can be useful for making statements about different experimental settings. Here, we capture this notion by formally defining the concept of operationally meaningful representations. We present an autoencoder architecture with attention mechanism that can generate such representations and demonstrate it on examples involving both classical and quantum physics. For instance, our architecture finds a compact representation of an arbitrary two-qubit system that separates local parameters from parameters describing quantum correlations.ISSN:2632-215
Entangling logical qubits with lattice surgery
The development of quantum computing architectures from early designs and current noisy devices to fully fledged quantum computers hinges on achieving fault tolerance using quantum error correction1,2,3,4. However, these correction capabilities come with an overhead for performing the necessary fault-tolerant logical operations on logical qubits (qubits that are encoded in ensembles of physical qubits and protected by error-correction codes)5,6,7,8. One of the most resource-efficient ways to implement logical operations is lattice surgery9,10,11, where groups of physical qubits, arranged on lattices, can be merged and split to realize entangling gates and teleport logical information. Here we report the experimental realization of lattice surgery between two qubits protected via a topological error-correction code in a ten-qubit ion-trap quantum information processor. In this system, we can carry out the necessary quantum non-demolition measurements through a series of local and entangling gates, as well as measurements on auxiliary qubits. In particular, we demonstrate entanglement between two logical qubits and we implement logical state teleportation between them. The demonstration of these operations—fundamental building blocks for quantum computation—through lattice surgery represents a step towards the efficient realization of fault-tolerant quantum computation.ISSN:0028-0836ISSN:1476-468