Stanford’s latest breakthrough: logical door calculation is super simple with light quantum!

Today’s many quantum computers are complicated, it is difficult to expand the scale, and it is necessary to run more colder than the interstellar space.These challenges cause researchers to explore the possibility of constructing quantum computers operating using photon (photon).Photons can easily transfer information from one place to another, and photonic quantum computers can operate at room temperature, so this method is very promising.However, although people have successfully created a separate quantum "logic gate", a large number of logical doors are constructed with photons and connect them in a reliable manner to perform complex calculations, or a technical problem.

Recently, Stanford University researchers have proposed a simpler photon quantum computer design, and can be used along the ready-made components. According to a paper published on Journal Optica on November 29, they proposed using lasers to manipulate individual atoms, while individual atoms can modify the state of photons by a phenomenon called "quantum invisible path". The atom can also be reset and reused in many quantum doors, so that there is no need to construct a plurality of different physical doors, which greatly reduces the complexity of constructing light quantum computers.

"Normally, if you want to build this type of quantum computer, you must use thousands of quantum transmitters to keep them perfect, then integrated into a huge photon circuit," application physics doctoral student The first author BEN BEN BARTLETTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTLET, and we only need a few relatively simple components, and the size of the machine does not increase with the size of the quantum program you want to run. " A very simple design requires only several devices: fiber optic cable, beam splitter, a pair of optical switches and optical cavities.

Fortunately, these components already exist and are already commercially used and continuously improved because they are currently used in quantum calculations. For example, telecommunications companies have been committed to improving fiber optic cables and optical switches. "The proposal of this program is based on people’s efforts and investment in people who have made these components. The professor of Stanford Engineering, Shanhui Fan, senior author of the papers. "They are not new components specifically used for quantum computing."

New design

The design of Stanford scientists consists of two main parts: a storage ring and a scattering unit.The function of the memory ring is similar to the memory in the normal computer, which is a fiber loop including a plurality of photons propagated around the loop. Similar to the bit of storage information in the classic computer, in this system, each photon represents a quantum bit. The photons determine the value of the quantum bits around the traveling direction of the storage ring, which may be 0 or 1. Further, since the photon is in the superimposed state, a single photon can simultaneously flow in both directions, which means the value of the combination of 0 and 1.

Figure 1. Photon quantum computer architecture described in this work.

(a) Physical design of the equipment. The photon quantum bit is reversely propagated by the fiber storage ring, and the optical switch can selectively guide the photon interaction with the atomic interaction in the cavity by the scattering unit, and the cavity is coherentiated in the cavity.

(b) The energy structure of the atom: ω1 is resonant to the cavity mold and the photon carrier frequency, and ω0 is far apart.

(c) the description of the BLOCH sphere on the photon quantum bit state {|?, |?} foundation and an operation applying the scattering unit. About rotation

Progressor and beam splitter apply a fixed angle (gray), and rotate

Apply a cavity laser using a lumen laser using a controlled angle θ (pure red). The projection measuring atom transmits this to the photon, but may exceed the target angle θ through π (red dashed line) depends on the measurement result m. ??This operation is a universal original single quantum bit: By combining multiple such operations, and The subsequent rotation angle is adjusted according to the measurement results, and any single quantum ratio can be determined.

The researchers can manipulate photons by directing photons from the memory ring to the scattering unit, where it propagates to cavities containing a single atom. The photon is then interacting with atoms, resulting in "entanglement", which is a quantum, and two particles can even affect each other at a very far distance. Then, the photon returns the storage ring, and then the state of the atom is changed again. Because the atoms and photons are entangled, the operation of the atom will also affect the state of their pairing photons.

Figure 2. Quantum gate sequence corresponding to photons pass through the scattering unit. The projection measurement will be transferred to the photon quantum bits to the rotation of atom quantum bits.

"By measuring the state of the atom, you can transfer the operation to the photon," Ben Bartlett said. "So we only need a controllable atom quantum bit, we can use it as a proxy to indirect all other photon quantum bits.

Because any quantum logic door can be compiled into a series of operations performed on a single particle, in principle, you can use only one controllable "atomic agent quantum bit" to run any size quantum program. In order to run the program, the code is converted to a series of operations, which guides the photon to the scattering unit and manipulate the atom quantum bit. Because you can control atoms and photon interactions, the same device can run many different quantum programs.

Figure 3. Conceptual diagram of the instruction sequence to compile the quantum circuit into the device to be executed on the device.

(a) Universal target quantum circuit.

(b) Decompose the equivalent circuit and the CσZ door of single quantum bit.

(c) The circuit is further decomposed into a series of scattering interactions. This sequence can be assembled into a command set on the classic computer, including six different primitives corresponding to physical actions.

(d) The controllable elements of the quantum device are optical switches, cavity lasers and atomic states.

"For many photon quantum computers, the physical structure passed by photons represents different logic doors, so if you want to change the running program, it usually involves physically reconfiguring hardware," Bartlett said. "And under this new design, you don’t need to change hardware, just need to give a different set of instructions for machines."