Emanuel Knill
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View article: Constructing an approximate logical Markovian model of consecutive QEC cycles of a stabilizer code
Constructing an approximate logical Markovian model of consecutive QEC cycles of a stabilizer code Open
As quantum error correction (QEC) experiments continue to make rapid progress, there is increased interest in designing experiments with guarantees of logical performance. At present, one difficulty is the lack of a clear connection betwee…
View article: Broadband pulsed quadrature measurements with calorimeters
Broadband pulsed quadrature measurements with calorimeters Open
A general one-dimensional quantum optical mode is described by a shape in the time or frequency domain. A fundamental problem is to measure a quadrature operator of such a mode. If the shape is narrow in frequency this can be done by pulse…
View article: Traceable random numbers from a nonlocal quantum advantage
Traceable random numbers from a nonlocal quantum advantage Open
The unpredictability of random numbers is fundamental to both digital security and applications that fairly distribute resources. However, existing random number generators have limitations-the generation processes cannot be fully traced, …
View article: Multi-mode Gaussian State Analysis with one Bounded Photon Counter
Multi-mode Gaussian State Analysis with one Bounded Photon Counter Open
Gaussian states are ubiquitous in quantum optics and information processing, and it is essential to have effective tools for their characterization. One such tool is a photon-number-resolving detector, and the simplest configuration involv…
View article: Completing fault models for abductive diagnosis
Completing fault models for abductive diagnosis Open
In logic-based diagnosis, the consistency-based method is used to determine the possible sets of faulty devices. If the fault models of the devices are incomplete or nondeterministic, then this method does not necessarily yield abductive e…
View article: Traceable Device-Independent Randomness as a Service
Traceable Device-Independent Randomness as a Service Open
We implement a traceable protocol for device-independent random number generation. Our demonstration involves transparently integrating a device-independent RNG into a public randomness beacon, and feeding 7434 random number pulses into th…
View article: Optimized experiment design and analysis for fully randomized benchmarking
Optimized experiment design and analysis for fully randomized benchmarking Open
Randomized benchmarking (RB) is a widely used strategy to assess the quality of available quantum gates in a computational context. RB involves applying known random sequences of gates to an initial state and using the statistics of a fina…
View article: An atomic boson sampler
An atomic boson sampler Open
A boson sampler implements a restricted model of quantum computing. It is defined by the ability to sample from the distribution resulting from the interference of identical bosons propagating ac- cording to programmable, non-interacting d…
View article: An atomic boson sampler
An atomic boson sampler Open
A boson sampler implements a restricted model of quantum computing. It is defined by the ability to sample from the distribution resulting from the interference of identical bosons propagating according to programmable, non-interacting dyn…
View article: Towards a resolution of the spin alignment problem
Towards a resolution of the spin alignment problem Open
Consider minimizing the entropy of a mixture of states by choosing each state subject to constraints. If the spectrum of each state is fixed, we expect that in order to reduce the entropy of the mixture, we should make the states less dist…
View article: Multi-mode Gaussian state analysis with total-photon counting
Multi-mode Gaussian state analysis with total-photon counting Open
The continuing improvement in the qualities of photon-number-resolving (PNR) detectors opens new possibilities for measuring quantum states of light. In this work we consider the question of what properties of an arbitrary multi-mode Gauss…
View article: Constraints on Gaussian error channels and measurements for quantum communication
Constraints on Gaussian error channels and measurements for quantum communication Open
Joint Gaussian measurements of two quantum systems are important for quantum communication between remote parties and are often used in continuous-variable teleportation or entanglement-swapping protocols. Many of the errors in real-world …
View article: Serving Verifiable, Device-Independent Randomness to the Public
Serving Verifiable, Device-Independent Randomness to the Public Open
Device-independent random number generators can be certified unhackable simply by the impossibility of superluminal signaling. We demonstrate a novel protocol to transparently operationalize this security through a public randomness beacon…
View article: Confidence-Interval Construction with Non-I.I.D. Spot-Checking Trials & its Application in Quantum Information
Confidence-Interval Construction with Non-I.I.D. Spot-Checking Trials & its Application in Quantum Information Open
We develop a method to estimate the sum of conditional means of a sequence of random variables given our access to only a subsequence by spot-checking. The method works with non-independent-and-identically-distributed (non-i.i.d.) random v…
View article: Multi-mode Gaussian State Analysis with Total Photon Counting
Multi-mode Gaussian State Analysis with Total Photon Counting Open
The continuing improvement in the qualities of photon-number-resolving detectors opens new possibilities for measuring quantum states of light. In this work we consider the question of what properties of an arbitrary multimode Gaussian sta…
View article: Constraints on Gaussian Error Channels and Measurements for Quantum Communication
Constraints on Gaussian Error Channels and Measurements for Quantum Communication Open
Joint Gaussian measurements of two quantum systems can be used for quantum communication between remote parties, as in teleportation or entanglement swapping protocols. Many types of physical error sources throughout a protocol can be mode…
View article: Improving quantum state detection with adaptive sequential observations
Improving quantum state detection with adaptive sequential observations Open
For many quantum systems intended for information processing, one detects the logical state of a qubit by integrating a continuously observed quantity over time. For example, ion and atom qubits are typically measured by driving a cycling …
View article: High-Fidelity Indirect Readout of Trapped-Ion Hyperfine Qubits
High-Fidelity Indirect Readout of Trapped-Ion Hyperfine Qubits Open
We propose and demonstrate a protocol for high-fidelity indirect readout of trapped ion hyperfine qubits, where the state of a $^9\text{Be}^+$ qubit ion is mapped to a $^{25}\text{Mg}^+$ readout ion using laser-driven Raman transitions. By…
View article: Improving quantum state detection with adaptive sequential observations
Improving quantum state detection with adaptive sequential observations Open
For many quantum systems intended for information processing, one detects the logical state of a qubit by integrating a continuously observed quantity over time. For example, ion and atom qubits are typically measured by driving a cycling …
View article: Scalable multiphoton quantum metrology with neither pre- nor post-selected measurements
Scalable multiphoton quantum metrology with neither pre- nor post-selected measurements Open
The quantum statistical fluctuations of electromagnetic fields establish a limit, known as the shot-noise limit, on the sensitivity of optical measurements performed with classical technologies. However, quantum technologies are not constr…
View article: Direct observation of deterministic macroscopic entanglement
Direct observation of deterministic macroscopic entanglement Open
Quantum entanglement goes large Quantum entanglement occurs when two separate entities become strongly linked in a way that cannot be explained by classical physics; it is a powerful resource in quantum communication protocols and advanced…
View article: Multiphoton quantum metrology with neither pre- nor post-selected measurements
Multiphoton quantum metrology with neither pre- nor post-selected measurements Open
The quantum statistical fluctuations of the electromagnetic field establish a limit, known as the shot-noise limit, on the sensitivity of optical measurements performed with classical technologies. However, quantum technologies are not con…
View article: Tomography of Entangled Macroscopic Mechanical Objects
Tomography of Entangled Macroscopic Mechanical Objects Open
Observing quantum mechanics at the macroscopic scale has captured the attention of scientists and the imagination of the public for more than a century. While quantum mechanics was conceived in the context of electrons and atoms, the abili…
View article: Direct observation of deterministic macroscopic entanglement
Direct observation of deterministic macroscopic entanglement Open
Quantum entanglement of mechanical systems emerges when distinct objects move with such a high degree of correlation that they can no longer be described separately. Although quantum mechanics presumably applies to objects of all sizes, di…
View article: Certified quantum measurement of Majorana fermions
Certified quantum measurement of Majorana fermions Open
We present a quantum self-testing protocol to certify measurements of fermion parity involving Majorana fermion modes. We show that observing a set of ideal measurement statistics implies anti-commutativity of the implemented Majorana ferm…
View article: Experimental Low-Latency Device-Independent Quantum Randomness
Experimental Low-Latency Device-Independent Quantum Randomness Open
Applications of randomness such as private key generation and public randomness beacons require small blocks of certified random bits on demand. Device-independent quantum random number generators can produce such random bits, but existing…
View article: Efficient randomness certification by quantum probability estimation
Efficient randomness certification by quantum probability estimation Open
For practical applications of quantum randomness generation, it is important to certify and further produce a fixed block of fresh random bits with as few trials as possible. Consequently, protocols with high finite-data efficiency are pre…
View article: Quantum gate teleportation between separated qubits in a trapped-ion processor
Quantum gate teleportation between separated qubits in a trapped-ion processor Open
Teleporting a trapped-ion quantum gate Gating—controlling the state of one qubit conditioned on the state of another—is a key procedure in all quantum information processors. As the scale of quantum processors increases, the qubits will ne…
View article: Quantum process fidelity bounds from sets of input states
Quantum process fidelity bounds from sets of input states Open
We investigate the problem of bounding the quantum process fidelity given bounds on the fidelities between target states and the action of a process on a set of pure input states. We formulate the problem as a semidefinite program and prov…