Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userQuantum State Readout, Collapses, Probes and Signals
146
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Theories involving localized collapse allow the possibility that classical information could be obtained about quantum states without using POVMS and without allowing superluminal signalling. We can model this by extending quantum theory to include hypothetical devices that read out information about the local quantum state at a given point, defined by considering only collapses in its past light cone. Like Popescu-Rohrlich boxes, these hypothetical devices would have practical and scientific implications if realisable. These include signalling through opaque media, probing the physics of distant or opaque systems without needing a reflected signal and giving detailed information about collapse dynamics without requiring direct observation of the collapsing system. These potential applications motivate systematic searches for possible signatures of these nonstandard extensions of quantum theory, and in particular for relevant gravitational effects, such as the validity of semi-classical gravity on small scales.
rate research
Read More
Quantum state measurement is not only a fundamental component of quantum physics, but also plays an important role in the development of various practical quantum technologies, including quantum communication, quantum computing, as well as quantum metrology. However, the fidelity of readout exponentially decays with the number of qubits, which would hinder the large-scale expansion of quantum information processing. In particular, qubit measurement is generally the most error-prone operation on a quantum computer. Here, we present a quantum state readout method, named compression readout, to avoid huge errors caused by multi-qubit measurement, by compressing the quantum state into a single ancilla qubit and measuring this ancilla qubit. Compared with conventional measurements, our method is significantly more resilient against the readout noise from qubit growth, making it a promising candidate for high-fidelity quantum state readout in large-scale quantum computing.
We propose a procedure for tomographic characterization of continuous variable quantum operations which employs homodyne detection and single-mode squeezed probe states with a fixed degree of squeezing and anti-squeezing and a variable displacement and orientation of squeezing ellipse. Density matrix elements of a quantum process matrix in Fock basis can be estimated by averaging well behaved pattern functions over the homodyne data. We show that this approach can be straightforwardly extended to characterization of quantum measurement devices. The probe states can be mixed, which makes the proposed procedure feasible with current technology.
Robust, high-fidelity readout is central to quantum device performance. Overcoming poor readout is an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. Spin defects in solids combine the repeatability and precision available to atomic and cryogenic systems with substantial advantages in compactness and range of operating conditions. However, in spite of experimental progress in specific systems, solid-state spin sensors still lack a universal, high-fidelity readout technique. Here we demonstrate high-fidelity, room-temperature readout of an ensemble of nitrogen-vacancy (NV) centers via strong coupling to a dielectric microwave cavity, building on similar techniques commonly applied in cryogenic circuit cavity quantum electrodynamics. This strong collective interaction allows the spin ensembles microwave transition to be probed directly, thereby overcoming the optical photon shot noise limitations of conventional fluorescence readout. Applying this technique to magnetometry, we show magnetic sensitivity approaching the Johnson-Nyquist noise limit of the system. This readout technique is viable for the many paramagnetic spin systems that exhibit resonances in the microwave domain. Our results pave a clear path to achieve unity readout fidelity of solid-state spin sensors through increased ensemble size, reduced spin-resonance linewidth, or improved cavity quality factor.
We address the impossibility of achieving exact time reversal in a system with many degrees of freedom. This is a particular example of the difficult task of aiming an initial classical state so as to become a specific final state. We also comment on the classical-to-quantum transition in any non-separable closed system of $n geq 2$ degrees of freedom. Even if the system is initially in a well defined WKB, semi-classical state, quantum evolution and, in particular, multiple reflections at classical turning points make it completely quantum mechanical with each particle smeared almost uniformly over all the configuration space. The argument, which is presented in the context of $n$ hard discs, is quite general. Finally, we briefly address more complex quantum systems with many degrees of freedom and ask when can they provide an appropriate environment to the above simpler systems so that quantum spreading is avoided by continuously leaving imprints in the environment. We also discuss the possible connections with the pointer systems that are needed in the quantum-to-classical collapse transitions.
We propose and analyze a high fidelity readout scheme for a single instance approach to quantum computing in rare-earth-ion-doped crystals. The scheme is based on using different species of qubit and readout ions, and it is shown that by allowing the closest qubit ion to act as a readout buffer, the readout error can be reduced by more than an order of magnitude. The scheme is shown to be robust against certain experimental variations, such as varying detection efficiencies, and we use the scheme to predict the expected quantum fidelity of a CNOT gate in these solid state systems. In addition, we discuss the potential scalability of the protocol to larger qubit systems. The results are based on parameters which we believed are experimentally feasible with current technology, and which can be simultaneously realized.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
