Qubit

About: Qubit is a research topic. Over the lifetime, 29978 publications have been published within this topic receiving 723084 citations. The topic is also known as: quantum bit & qbit.

In situ single-atom array synthesis using dynamic holographic optical tweezers.

Abstract: Establishing a reliable method to form scalable neutral-atom platforms is an essential cornerstone for quantum computation, quantum simulation and quantum many-body physics. Here we demonstrate a real-time transport of single atoms using holographic microtraps controlled by a liquid-crystal spatial light modulator. For this, an analytical design approach to flicker-free microtrap movement is devised and cold rubidium atoms are simultaneously rearranged with 2N motional degrees of freedom, representing unprecedented space controllability. We also accomplish an in situ feedback control for single-atom rearrangements with the high success rate of 99% for up to 10 μm translation. We hope this proof-of-principle demonstration of high-fidelity atom-array preparations will be useful for deterministic loading of N single atoms, especially on arbitrary lattice locations, and also for real-time qubit shuttling in high-dimensional quantum computing architectures. It would be desirable to have a reliable and scalable method to manipulate neutral-atoms for the creation of controllable quantum systems. Here the authors demonstrate real-time transport of single rubidium atoms in holographic microtraps controlled by liquid-crystal spatial light modulators.

Sub-millihertz magnetic spectroscopy with a nanoscale quantum sensor

Abstract: Precise timekeeping is critical to metrology, forming the basis by which standards of time, length and fundamental constants are determined. Stable clocks are particularly valuable in spectroscopy as they define the ultimate frequency precision that can be reached. In quantum metrology, where the phase of a qubit is used to detect external fields, the clock stability is defined by the qubit coherence time, which determines the spectral linewidth and frequency precision. Here we demonstrate a quantum sensing protocol where the spectral precision goes beyond the sensor coherence time and is limited by the stability of a classical clock. Using this technique, we observe a precision in frequency estimation scaling in time $T$, as $T^{-3/2}$ for classical oscillating fields. The narrow linewidth magnetometer based on single spins in diamond is used to sense nanoscale magnetic fields with an intrinsic frequency resolution of 607 $\mu$Hz, 8 orders of magnitude narrower than the qubit coherence time.

Additivity for a class of unital qubit channels

Abstract: Additivity of the Holevo capacity is proved for product channels, under the condition that one of the channels is in a certain class of unital qubit channels, with the other completely arbitrary. This qubit class includes the depolarizing channel. As a byproduct this proves that the Holevo bound is the ultimate information capacity of such qubit channels (assuming no prior entanglement between sender and receiver). Additivity of minimal entropy and multiplicativity of p-norms are also proved under the same assumptions.

The role of quantum measurement in stochastic thermodynamics

Abstract: This article sets up a new formalism to investigate stochastic thermodynamics in the quantum regime, where stochasticity and irreversibility primarily come from quantum measurement. In the absence of any bath, we define a purely quantum component to heat exchange, that corresponds to energy fluctuations caused by quantum measurement. Energetic and entropic signatures of measurement-induced irreversibility are then explored for canonical experiments of quantum optics, and the energetic cost of counter-acting decoherence is studied on a simple state-stabilizing protocol. By placing quantum measurement in a central position, our formalism contributes to bridge a gap between experimental quantum optics and quantum thermodynamics, and opens new paths to characterize the energetic features of quantum processing. Measuring a quantum system is an ultimately random operation. It induces a genuinely quantum time arrow, increasing the system’s entropy. But because it perturbs its state, quantum measurement also provides energy to the quantum system. These energetic quantum fluctuations play the same role as thermal fluctuations in thermodynamics, while being of quantum nature. Building on such “Quantum Heat”, a group of scientists from france provided a thermodynamic analyzis of canonical experiments of quantum optics. They show that quantum heat is a major concept to evaluate the performances of a basic protocol to counteract the decoherence of a quantum bit. The findings pave the way towards a new generation of quantum engines, powered by quantum measurement. They bring new tools to investigate the energetic cost of quantum protocols performed at ultra-low temperature, in the presence of decoherence.

Adiabatic quantum computation with superconducting qubits

Abstract: A method for computing using a quantum system (1540) comprising a plurality of superconducting qubits is provided. Quantum system (1540) can be in any one of at least two configurations including (i) an initialization Hamiltonian Ho and (ii) a problem Hamiltonian Hp. The plurality of superconducting qubits are arranged with respect to one another, with a predetermined number of couplings between respective pairs of superconducting qubits in the plurality of qubits, such that the plurality of superconducting qubits, coupled by the predetermined number of couplings, collectively define a computational problem to be solved. In the method, quantum system (1540) is initialized to the initialization Hamiltonian Ho. Quantum system (1540) is then adiabatically changed until it is described by the ground state of the problem Hamiltonian Hp. The quantum state of quantum system (1540) is then readout thereby solving the computational problem to be solved.