No abstract

Information was stored as quantum phase in an N-state Rydberg atom data register. One or more flipped states stored in an eight-state atomic wave packet could be retrieved in a single operation, in agreement with a recent proposal by Grover.Storage of information as quantum phase was first proposed several years ago in connection with a new class of computational algorithms based on the rules of quantum mechanics rather than classical physics (1). The analog of the binary bit, which is the smallest piece of classical information, is the two-level quantum system, or qubit (2). Introductions to this subject often begin with the observation that a qubit differs from a bit because it can be prepared in more than two different states (3). For example, if the two levels are designated ͉0͘ and ͉1͘, then superpositions such as [͉0͘ ϩ exp(i)͉1͘]/ ͌ 2 are possible states of the qubit. Here, the real number is the quantum phase difference between probability amplitudes of the two levels in the superposition. Thus quantum phase is present in quantum algorithms, and its maintenance, control, and measurement may be essential factors in the performance of quantum computations.One example of an algorithm where quantum phase plays an essential role is the database search problem proposed by Grover (4, 5). Grover's search differs from some other quantum algorithms because it does not require any nonlocal entanglement of different degrees of freedom in the system. If information is stored as phase, then the superposition principle of quantum mechanics provides an efficient method to search the database (6). Superposition is also present in some classical analog data storage media, such as optical holograms, which use the classical phases of interfering electromagnetic waves; however, quantum systems contain the additional nonclassical feature of wave function collapse after a measurement.In his original paper on this subject, Grover asked the following question: When an N-state quantum register (composed of log 2 N qubits) is prepared with one state phase-shifted from all the others, how many operations does it take to find the flipped state (4)? Grover's algorithm takes only order ͌ N steps, whereas classical algorithms require order N/2 steps. The algorithm performs an inversion about the average defined by the following unitary operation D on the N-element state vector:This operation amplifies the flipped state and attenuates the others. There have been several recent demonstrations of this search, using qubit systems based on magnetic resonance (7,8) or photon interference (9). Grover's second paper considers the case when the database is capable of receiving a single query on all of its states simultaneously. This produces a large payoff in parallelism: The search algorithm now takes only a single quantum operation (5).We have investigated the storage and retrieval of information in the quantum phase of a coherent superposition state of energy levels in a highly excited atom. Two situations were examined. First, we prepared a...

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.

No abstract

Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation that captures essential information from the complexities. Here, we find that thermalization of an isolated many-body quantum state can be described by a master equation. We observe sudden quench dynamics of quantum Ising-like models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg-atom interaction. Saturation of their local observables, a thermalization signature, obeys a master equation experimentally constructed by monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance. Our experiment agrees with theories and demonstrates the detailed balance in a thermalization dynamics that does not require coupling to baths or postulated randomness.