Fermionic Bell-State Analyzer for Spin Qubits

Engel, Hans–Andreas; Loss, Daniel

doi:10.1126/science.1113203

Cited by 97 publications

(111 citation statements)

References 30 publications

(32 reference statements)

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“…A single charge measurement on one dot collapses the wave function to the corresponding spin state, realizing a spin to charge conversion. There exist several alternative schemes, [40][41][42][43] some of them being pursued experimentally. 24,25,44 We construct an effective, four state ͑two spin and two sites͒ tunneling Hamiltonian for the single-electron double dot system, which takes into effect the above results.…”

Section: Introductionmentioning

confidence: 99%

Spin-orbit effects in single-electron states in coupled quantum dots

2005

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Spin-orbit effects in single-electron states in laterally coupled quantum dots in the presence of a perpendicular magnetic field are studied by exact numerical diagonalization. Dresselhaus ͑linear and cubic͒ and Bychkov-Rashba spin-orbit couplings are included in a realistic model of confined dots based on GaAs. Group theoretical classification of quantum states with and without spin-orbit coupling is provided. Spin-orbit effects on the g factor are rather weak. It is shown that the frequency of coherent oscillations ͑tunneling amplitude͒ in coupled dots is largely unaffected by spin-orbit effects due to symmetry requirements. The leading contributions to the frequency involves the cubic term of the Dresselhaus coupling. Spin-orbit coupling in the presence of a magnetic field leads to a spin-dependent tunneling amplitude, and thus to the possibility of spin to charge conversion, namely, spatial separation of spin by coherent oscillations in a uniform magnetic field. It is also shown that spin hot spots exist in coupled GaAs dots already at moderate magnetic fields, and that spin hot spots at zero magnetic field are due to the cubic Dresselhaus term only.

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Section: Introductionmentioning

confidence: 99%

Spin-orbit effects in single-electron states in coupled quantum dots

2005

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“…Using this parity meter, a measurementbased CNOT gate for free "flying" electrons was designed. Following this result, implementations of a parity gate for spin [11] and charge qubits [12] have been proposed.…”

Section: Introductionmentioning

confidence: 99%

“…[10]. We also propose a possible realization of such a S − T 0 CNOT on double quantum dots using a recently proposed spin-parity meter [11].…”

Section: Introductionmentioning

confidence: 99%

Controlled-NOT gate for multiparticle qubits and topological quantum computation based on parity measurements

2008

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We discuss a measurement-based implementation of a controlled-NOT (CNOT) quantum gate. Such a gate has recently been discussed for free electron qubits. Here we extend this scheme for qubits encoded in product states of two (or more) spins-1/2 or in equivalent systems. The key to such an extension is to find a feasible qubit-parity meter. We present a general scheme for reducing this qubit-parity meter to a local spin-parity measurement performed on two spins, one from each qubit. Two possible realizations of a multiparticle CNOT gate are further discussed: electron spins in double quantum dots in the singlet-triplet encoding, and ν = 5/2 Ising non-Abelian anyons using topological quantum computation braiding operations and nontopological charge measurements.

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“…Some measurement-based schemes rely on the creation of highly-entangled cluster states (Raussendorf and Briegel 2001), which could be generated in quantumdot arrays using the Heisenberg exchange interaction . Other measurment-based schemes generate entanglement through partial Bellstate (parity) measurements (Beenakker et al 2004), which could also be implemented for spins in quantum dots using spin-to-charge conversion (Engel and Loss 2005). Independent of the method used, the generation or purification and subsequent detection of entangled electron spins would present a significant milestone on the road to a working quantum-dot quantum computer.…”

Section: Entanglement Generation Distil-lation and Detectionmentioning

confidence: 99%

Quantum Computing with Spins in Solids

Coish

Loss

2007

Handbook of Magnetism and Advanced Magnetic Materials

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The ability to perform high-precision one-and two-qubit operations is sufficient for universal quantum computation. For the Loss-DiVincenzo proposal to use single electron spins confined to quantum dots as qubits, it is therefore sufficient to analyze only single-and coupled double-dot structures, since the strong Heisenberg exchange coupling between spins in this proposal falls off exponentially with distance and long-ranged dipolar coupling mechanisms can be made significantly weaker. This scalability of the Loss-DiVincenzo design is both a practical necessity for eventual applications of multi-qubit quantum computing and a great conceptual advantage, making analysis of the relevant components relatively transparent and systematic. We review the Loss-DiVincenzo proposal for quantum-dot-confined electron spin qubits, and survey the current state of experiment and theory regarding the relevant single-and double-quantum dots, with a brief look at some related alternative schemes for quantum computing.

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Fermionic Bell-State Analyzer for Spin Qubits

Cited by 97 publications

References 30 publications

Spin-orbit effects in single-electron states in coupled quantum dots

Spin-orbit effects in single-electron states in coupled quantum dots

Controlled-NOT gate for multiparticle qubits and topological quantum computation based on parity measurements

Quantum Computing with Spins in Solids

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