Квантуйте апельсины бочками

Периодически пытаюсь сформулировать в доступной форме, чем же квантовый компьютер отличается от обыкновенного. Может быть и сам пойму наконец. :)

Обычный компьютер хранит и оперирует битами. В каждый бит можно записать и прочитать нолик или единичку. В процессе работы компьютер преобразует эти биты по установленным правилам, на каждом шаге довольно несложным. Классические формулы булевой логики или арифметики, оперирующие двоичными цифрами.

Квантовый компьютер оперирует, понятное дело, квантовыми битами: для краткости qubit или кубит. В кубит можно ровно так же записать и прочитать нолик или единичку. В процессе вычисления кубиты тоже преобразуются по заданным правилам, заданным программой. Формулы этих преобразований тоже довольно простые. Но только каждый кубит в них выглядит не как двоичная цифра, а как комплексное число. При считывании результата квадрат этого числа превращается в вероятность получить единичку на выходе.

На самом деле ничего вероятностного в квантовом компьютере нет. "Правильное" вычисление строится так, чтобы на выходе всегда был детерминированный бинарный результат. Фишка же в том, что квантовое вычисление получается в пределе бесконечно мощнее классического. В частности, можно за полиномиальное время решать NP-полные задачи.

Из истории вещания в Bay area

Перепост от Oleg Zabluda: https://plus.google.com/112065430692128821190/posts/UhDRr9R1ZgN

1941: [...] the transmitter was moved to the eastern tip of Redwood Peninsula (now Redwood City) three “curtain” antennas for 19, 25 and 49 meters, were perfectly aligned (126/306 degrees) with the capitals of Latin America and Asia. In fact a perfectly straight line could (and still can) be drawn from Tokyo, San Francisco, Mexico City, Quito and Buenos Aires! In the days of relatively uncluttered HF bands, the 50 kw signal was heard with great clarity, virtually around the world.
http://bayarearadio.org/schneider/kgei/kgei.shtml

KPO flat-top antenna antenna system Circa 1930s.
The two towers supported the [single-wire] flat-top "T" antenna, which was oriented East-West. The concrete building between the towers held the antenna tuning network. [...] The original KNBC-FM antenna can be seen mounted atop the East tower.
http://bayarearadio.org/schneider/radio079.shtml
http://bayarearadio.org/schneider/radio002.shtml

KNBC converted from a flat-top antenna to a Franklin antenna in 1949. The west tower of the flat-top antenna was toppled to make room for the new tower. The east tower was used as a temporary antenna during the construction, and continues to stand today as KNBR's emergency backup antenna.
http://bayarearadio.org/schneider/radio095.shtml

KNBR's present 550-foot transmitter tower was completed in 1949 when the station was known as KNBC. (It had been KPO until 1947.) This type of antenna is called a Franklin antenna, a design used by only a few AM stations in the U.S. The antenna is easily recognized by the porcelain insulator in the middle of the structure.

A traditional Franklin antenna consists of two half wave antennas stacked end-to-end and fed in phase. At 680 kc, this would require a tower 1,500 ft. tall, an obvious impracticality. The KNBC tower measures 400 ft. to the midpoint insulator. The upper portion of the tower is shortened to only 150 ft., and this is compensated for by a 50 ft. diameter capacitive top loading "hat" at the top of the structure. The top section is fed from a shunt tap on the lower section. There is a copper tube that runs up from the tap on insulated stand-offs, where it connects to the upper section just above the insulator.

The Franklin Antenna is used as a means to lower the radiation angle of the signal. This increases the ground wave coverage of the station, and reduces the night time interference at the fringes of the ground wave signal, caused by sky wave signals originating from the same tower.
http://bayarearadio.org/schneider/radio019.shtml

NBC changed the call letters of KPO to KNBC on November 23, 1947. In 1949 a new 550-foot tower was constructed, replacing the longwire T-type antenna that had been in use at the Belmont transmitter site since 1933. [...] In the early 1960s, NBC wanted to move the KNBC call letters to its Los Angeles TV station KRCA, [...] As a result, the call letters of its San Francisco radio station were changed once again, this time from KNBC to KNBR.
http://bayarearadio.org/schneider/kpo.shtml

Aerial view of KGEI, Redwood City, California in July of 1968. KGEI, purchased by FEBC in 1960, and closed in 1995, [...] KGEI shared some 50 acres with local NBC station KNBR, whose AM towers are seen in the upper right near the HAZard signs. Three 125 foot towers and barely visible poles on the right support the three short wave arrays. KGEI's building is the smaller building on the left. Also barely visible on the lower right is a small guard shack, occupied by Marines during WWII. .45 caliber bullets can still be dug out of the dikes.
http://www.theradiohistorian.org/kgei9.htm
http://bayarearadio.org/schneider/kgei/images/F01277_KGEIAntennas_FS.jpg

Google Maps: KNBR
http://www.fybush.com/sites/2005/site-051021.html
http://bayarearadio.org/stn_photos/kgei_xmtr-site_2004.shtml