Quantum Computing Progress and Prospects (2019) / Chapter Skim
Currently Skimming:
Appendix D: Other Approaches to Building Qubits
Appendix D: Other Approaches to Building Qubits
Pages 212-225
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 212... ...
D.1 PHOTONIC QUANTUM COMPUTATION Photons have some properties that make them extremely attractive for use in quantum computers: photons interact relatively weakly with their environment and with each other. This is the reason that photons can travel quite far in many materials without being scattered or absorbed, giving photonic qubits good coherence properties and making them useful for transmitting quantum information over long distances [1]
|
From page 213... ...
In linear optics quantum computing, an effective strong interaction is created by a combination of single-photon operations and measurements, which can be used to implement a two-qubit gate. A second approach, which uses optically active defects and quantum dots2 that interact strongly with photons to induce strong effective interactions between photons, is discussed in Section D.3.1 on optically gated semiconducting qubits.
|
From page 214... ...
. This approach has technological similarities to ion trap quantum computation, and uses optical and microwave pulses for qubit manipulation, with the potential for making individual arrays with up to a million qubits.
|
From page 215... ...
This is cold enough for most quantum computing schemes, but it is believed that the cooling can be improved significantly; theoreti cal cooling limits approach 100 percent ground state occupation. Because single-qubit gate times range from a few to a few hundred microseconds, in principle, on the order of 105 operations can be performed within the longest demonstrated decoherence times (these are best-case numbers)
|
From page 216... ...
D.3 SEMICONDUCTOR QUBITS Semiconductor qubits can be divided into two types, depending on whether they are manipulated optically or electrically. Optically gated semiconductor qubits typically use optically active defects or quantum dots that induce strong effective couplings between photons, while electrically gated semiconductor qubits use voltages applied to lithographically defined metal gates to confine and manipulate the electrons that form the qubits, a technology that is very similar to that used for current classical computing electronics.
|
From page 217... ...
Optically active quantum dots also have been demonstrated to have promise for applications requiring quantum coherence. Two-qubit gates have been implemented using tunnel couplings between quantum dots [29]
|
From page 218... ...
D.3.2 Electrically Gated Semiconductor Qubits Electrically gated semiconducting quantum computing technologies have the potential to scale up to extremely large number of qubits, because of the qubits' small size and because of the use of fabrication methods very similar to those used in classical electronics. Electrically gated semiconducting qubits are defined and manipulated by applying voltages to lithographically defined metal gates on semiconductor surfaces [36]
|
From page 219... ...
The first electrically gated semiconducting qubits were fabricated in heterostructures of gallium arsenide and aluminum gallium arsenide [40] , but in this materials system the decohering effects of the nuclear spins in the host material greatly complicated the implementation of high-fidelity gate operations.
|
From page 220... ...
Topological quantum computation enables operations on the physical qubits to have extremely high fidelities because the qubit operations are protected by topological symmetry implemented at the microscopic level. Topological protection of quantum information is also the basis underlying the surface code, so one can view topological quantum computation as the implementation of the error-correction mechanism into the microscopic physics instead of by application of an error-correction algorithm on nontopological qubits.
|
From page 221... ...
The unpaired Majorana fermions can be arbitrarily far apart, and recombining them requires modifying the quantum state of the entire length of the system, which makes the excitations extremely resistant to local perturbations. The interest in developing materials systems that can support Majorana zero modes was sparked by Kitaev's work (2003)
|
From page 222... ...
As discussed above, significant materials, fabrication, and measurement challenges must be overcome to demonstrate even single-qubit gates of a topological quantum computer. However, the possibility of being able to implement extremely high fidelity gates that do not require error correction, or require very little error correction, is strong motivation to pursue this approach, partly because of the challenges that arise in the implementation of quantum error correction and partly because the necessary processor sizes would be much smaller than those needed for error-corrected architectures.
|
From page 223... ...
Calusine, and D.D. Awschalom, 2011, Room temperature coherent control of defect spin qubits in silicon carbide, Nature 479:84-88.
|
From page 224... ...
Loss and D.P. DiVincenzo, 1998, Quantum computation with quantum dots, Physi cal Review A 57:120-126.
|
From page 225... ...
Freedman, 2017, Scalable designs for quasiparticle-poisoning-protected topological quantum computation with Majorana zero modes, Physical Review B 95:235305.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.