Two-dimensional transport and transfer of a single atomic qubit in optical tweezers

Abstract

Quantum computers have the capability of out-performing their classical counterparts for certain computational problems 1 . Several scalable quantum-computing architectures have been proposed. An attractive architecture is a large set of physically independent qubits arranged in three spatial regions where (1) the initialized qubits are stored in a register, (2) two qubits are brought together to realize a gate and (3) the readout of the qubits is carried out 2,3 . For a neutral-atom-based architecture, a natural way to connect these regions is to use optical tweezers to move qubits within the system. In this letter we demonstrate the coherent transport of a qubit, encoded on an atom trapped in a submicrometre tweezer, over a distance typical of the separation between atoms in an array of optical traps 4-6 . Furthermore, we transfer a qubit between two tweezers, and show that this manipulation also preserves the coherence of the qubit.In the quest for an implementation of a quantum computer, scalability is a major concern. In the trapped-ion approach (see for example ref. 7), a lot of effort is being devoted to building arrays of small ion traps 8 , and to moving ion qubits whilst avoiding heating and decoherence 9 . Neutral atoms also offer promising properties for the realization of large quantum registers. For example, one-or two-dimensional addressable arrays of dipole traps have been demonstrated using holographic techniques 4 , micro-fabricated elements 5 , or active rearrangement of single atoms 6,10 . An alternative approach is to use the Mott insulator transition to initialize a three-dimensional register by loading a Bose-Einstein condensate into an optical lattice 11 . Recent progress has shown subwavelength addressability in such a system 12 . To carry out quantum computations, however, an additional key feature is the ability to realize the gate between two arbitrary qubits of the register.Here we demonstrate a scheme where a neutral-atom qubit is transferred between two moving tweezers ('register' to 'moving head'), and then transported towards an interaction zone where the two-qubit gate should be implemented [13][14][15][16] . We show that these manipulations of the external degrees of freedom preserve the coherence of the qubit, and do not induce any heating. This transport in a moving tweezer is a promising alternative to the recently demonstrated transport of qubits in 'optical conveyor belts' 6,17 , or in state-dependent moving optical lattices 18 . Altogether, these results could pave the way towards a scalable neutral-atom quantum-computing architecture.

Rapid Production of Uniformly Filled Arrays of Neutral Atoms

“…Using optical tweezers, long-range interactions between neutral atoms have been harnessed via Rydberg blockade [3-5], and it is now possible to observe controlled interactions and interference between bosonic and fermionic atoms placed individually in their motional ground state [6][7][8]. While optical tweezer traps can be scaled to arrays [9][10][11][12], realizing an ordered array with a single atom per trap is difficult and is a problem of long-standing interest [13][14][15][16].…”

“…Using optical tweezers, long-range interactions between neutral atoms have been harnessed via Rydberg blockade [3-5], and it is now possible to observe controlled interactions and interference between bosonic and fermionic atoms placed individually in their motional ground state [6][7][8]. While optical tweezer traps can be scaled to arrays [9][10][11][12], realizing an ordered array with a single atom per trap is difficult and is a problem of long-standing interest [13][14][15][16].Early experiments with optical tweezers demonstrated sub-Poissonian atom-number statistics using light-assisted collisions that rapidly expel pairs of atoms, a process known as collisional blockade [17][18][19][20]. This has become a reliable method to isolate single atoms, as well as the basis for parity imaging in quantum-gas microscopes [1,2,17].…”

Single atoms in the ring lattice for quantum information processing and quantum simulation

“…where Ω is the oscillation frequency of the atom, the mass is m, and the extension of the ground state wave function is σ [31,32]. For our experimental parameters, kHz rotation rate of atoms could be obtained with this method.…”

Supraclassical measurement using single-atom control of an atomic ensemble

“…We assume that we can adiabatically shift the two state-dependent potentials which confine the register atoms by 2.5 μm, as this can be efficiently done with no significant heating or atom losses, while preserving the qubit state with a high fidelity, as shown in Refs. [19] and [21]. This enables splitting of the atom wave function vertically by a distance δz, and a δφ = mgδzt/ phase difference is induced by letting the probe evolve for a time t.…”